Ever heard of share cropping? How about debt bondage or wage slavery? Slavery takes many forms. Very few include open air slave markets.

Also, this post is about peasants. While they were certainly a form of slave, particularly serfs, I have a suspicion you didn't know that and didn't intend to equivocate the two. Peasants weren't really bought or sold either. I'm sure it happened sometimes but it wasn't a structural component of feudalism.

All this to say, what's your point?