Posting stuff for free is a good way to let people try you out before spending money on you (especially if you are a new artist.) I put up a couple things for free at the marketplace so people can get a taste of my teaching style. From a marketing standpoint, it is good advertising too because then you link them back to your website and social media to get some more exposure.
As for pricing, I try to price things fairly so that they get their moneys worth. When it comes to the market I price things as follows (this is a loose structure as there are variables as well.)
-Free: Stuff that I want to give away for the above reasons i mentioned in the post.
-0.99: I have never released anything this cheap, however if i do it will be a single move or effect with little or no additional applications. ( a single sleight for example)
-1.99-3.99: Any full length effect with a single application or idea taught with it. (I teach a control that includes a fun routine to go with it.)
-4.99-9.99: A single effect with several applications or bonus ideas included. (A full length effect like "Chicago Closer" that also teaches a deck switch application and is several phases long.)
-over 10.00: Usually if I post anything over 10 it is because there are several ideas or effects in question. (My "Tour de Force; Complete Edition" download is priced above 10 because i teach 6 full length routines there.)
Hope this helps. Again, these ideas are not a ridged structure so i sometimes change things in between. If an effect is super popular and worth it, I may put a single effect for over 10. just depends. I have noticed that the marketplace is very hard to sell for over 10 though... lol