As a recent buyer, I was pleasantly surprise that there was a feedback system in place. This allowed me to have make a purchase rather confidently.
As for having the seller, donate $10.00 to list an item for sale, I believe that the pro outweighs the cons.
Forums of all types and interest is mainly maintained by die-hard fanatics who pour their heart and soul. This form of forums exist for the fact that we congregate on common interest and share our opinions(good or bad). There are places/sites for profiteering but sites like PentaxForums, should not be the place for capitalism.
The donation is a great idea to generate funds to maintain the site.
Just wanted to put my 2 cents on this changes to the Market Place.