IMO, generally, the things that appear in the Marketplace on BC are well priced. We are all gear-heads or we wouldn't be here, so we're savvy with not only what stuff tends to sell for, but also what kind of price someone would be willing to pay. I would really hope that no one takes the you-know-what with their pricing.
Haggled marginally for things, knocking a bit off here and there, free postage etc. but generally buying and selling for a fair price.