I am not truly sure on the correct answer to this so I will just give my take on it. It comes down to ethics. Most magicians believe that when you buy an effect from a recognized dealer or from the author directly then you are also buying the right to perform that trick the way the author performed it. You are buying the right to go out and perform his effect in a similar manor to the way he does it. On the other hand some magicians believe that you are simply buying the secret and have the right to perform the steps or method of the performance but you have no right to his patter and presentation. I am a member of the second camp, I believe that you are not entitled to the artistic expression of another unless their is some form of legal document granting you that right. It is his intellectual property. But I see the method differently. By releasing his secret to anyone that purchases his video he is by that fact letting you in on a trade secret and since it is no longer a secret it can be used by you as you see fit. I only apply this to the sleights within the method and not the method as a whole. I will not teach another an effect that I did not come up with myself. I may however teach you the balance palm for instance as it is a sleight and not an effect all unto its own. Basically where I draw the line is this. To put this in other terms and draw an analogy. I will teach you a note(sleight of hand movement), not a song(series of movements that make an effect) and though I may perform the song I would never do it the way that the originator performed it without some sort of written contract stating I can do so. Now I may teach an effect that another came up with using a method that I originated. So I could teach you my cups and balls routine, but I would never teach you Dai Vernon's nor would I try to perform the cups and balls his way.
When dealing with ebay you will see another divide. This one revolves around the original author getting money for the effect. Some believe that buying Thread on ebay is not right and you have no right to that effect or method. The logic behind this is somewhere along the line someone go the trick for free or at a greatly reduced cost. It would be the same as me and 20 of my friends each pitching in a buck and learn an effect on the cheap or if I purchased it and then gave it to others at a buck a piece. Reselling is wrong in their eyes. In another persons view the person that sold the effect is transferring his rights to use the effect as he is selling it to another. And another opinion is that since you paid money you paid your dues and therefore you have the right to perform the effect. I personally avoid buying an effect from anywhere than a magic dealer or the original author when possible. The latter being a case where it is no longer in print or is discontinued. I will however buy gaffs on ebay as I am not buying an effect. some would even say that is wrong as the money didn't go to the creator of the gaff, but the way I look at it is that the gaff is no longer in the possession of the original purchaser so it is a transfer type of deal. This is different than the transfer of an effect because the person selling it no longer has the ability to use it. in other words you can't resell an idea.
All in all this comes down to morals that you hold yourself to. I do not wish to gain the ideas of others unless they give it to me. whether that is through there DVD in a magic shop on in their lecture or actually just say here tack this. money in this is not relevant to me. If they give it to me for free it is their choice. A price of nothing is still a price. This goes the same for a teacher that gives me his original material. Once again I refer you to my distinction above. When you buy from ebay ask yourself the ally question. If a guy walked up to me in an ally and said hey you want to buy this thread DVD or for that matter just the secret to thread for $5, would you fell moral doing so? I personally would not. In the end I believe the two to be the same thing. But i also believe that your morals and ethics are just that yours. I can not dictate them directly but i may not hang with someone that I feel is imoral either.
To give an extreme example. I have been performing a bill penetration for several years now it is something that I came up with on my own. Recently as I am getting back into magic a person who saw me perform it said hey I saw that on youtube, the guy called it Ghostbills. Curious, I went on youtube and found out that yes someone was doing something similar to my effect. The video credited Andrew Mayne. I thought nothing of it, since I created the effect that I performed. During a magic meeting we were doing a teach a trick and I had nothing prepared so I showed my bill penetration. Once again I thought nothing of it it is my effect I should be able to do as I wish with it. During the teaching session I even told people that there are other bill penetrations out their and one I was told of is Andrew Mayne's Ghostbills. After the meeting one of the members came up to me and told me that my handling is almost the same, I just do one thing different. A subtlety I use when displaying the bill. He had went to Andrew's lecture and learned it there, he even told me that Andrew had published the effect. I honestly didn't know. I heard of independent creation but never thought I would be in the situation myself. Most people would go about there busyness as it is their effect and they have nothing to be ashamed of. That is their morals on the situation. I unfortunately look at it differently. I have heard of Andrew, mainly because I am trying to create illusions and I have heard I should look into his DVDs on the subject, I respect Andrew, From what I have heard he is a great guy, and I know Andrew has never heard of me. I know that he did not steal my effect and I know that I did not steal his, but he came out with the effect publicly first. This is the same as many people in history Alexander Graham Bell, Darwin and so on. All created something that they publicized before others who where working on the same thing did. Now please understand me when I say this, I do not feel that I was in a competitive race to publicize anything with anyone else nor do I think that he was doing that either. Just making that clear as I don't want to sound like I am gripping about the situation or blamming him or something. I'm not. I'm just saying stuff happens, but I digress. The reason I am telling you this is that I am going this weekend to buy my 23rd copy of Ghostbills. I hold myself to a high moral and if someone published an effect that they came up with and I happened to have came out with the same effect and they didn't steal it from me, well kudos to them for having more marketing savvy than I do. I honestly never though that the penetration was anything more than what I did when I didn't have anything else prepared. Looks like I'm wrong.

Every person in that meeting is getting a copy of the effect that I should them because in my moral compass, it is Andrew's effect now not mine. And I had no right to give it to others. Since I did it unintentionally I hope this karmacally makes up for it. I do know one thing however. no matter how small I think an effect is I plan on videoing myself doing my material from now on. You never know when I may be able to make a video myself.
I guess the long and the short of it is, morals are something that you must hold yourself to. and in the words of Rob Roy "Honor is the only gift a man can give to himself." Hope a quoted that correctly.
Red