That is sad that you can't trust people at something like a sewing class.
As far as the non-profits selling online to get a higher price goes, why shouldn't they? The money goes to good causes and it's no different than anyone else who tries to get the best price possible. I actually like Goodwill's site. It gives me access to a far larger selection of machines than I would ever have if I only shopped local and the prices are still lower than your average Ebay seller wants.
I have had good luck locally too and do prefer it because then I don't have to pay shipping but it's nice to have the option.
Rodney