I don't think that this is a huge problem when it comes to selling relatively expensive and bulky items like bikes. First you get to buy see & try the bike. Most of the time the seller will not ship it. There is a huge incentive for telling the truth on a product you sell when you get to actually meet the buyer : it's an awkward moment for the seller when the latter realize, after a 30 min/1 hour trip that the item was not described accurately. I won't say that it never happened to me as a buyer but it certainly happens more often when you buy a used item that is shipped to your place.

Also the buyer knows where you live, and is relatelively close to your home. Some buyers being complete morons hidding the flaws of an item is definitely a bad idea.