+1 to
@t3chg33k's post.
I see no one brought this up: What about cases where the seller has no invoice? I don't think sellers always mention their buying price in such cases and neither do potential buyer's ask for it (or maybe they do, I'm not aware).
I'm all for transparency, but I'm not sure if enforcing this will add additional work for the mods or upset the MP ecosystem here. I mean, it's not difficult to ban masking, but handling what follows probably is. If a person is selling above/at his buying price, a bunch of users will crap on his thread for doing so and this will affect the sale temporarily. It's not his fault that he bought it during a sale or the market went downhill afterwards.
People are always going to sell according to the current market condition and that's not unfair of sorts. I fully respect the good samaritans who are not out to make a profit and stick to their principles (don't ask me what those are, it is
theirs), but they are far and few between. There's nothing wrong in someone trying to get a better price for their product than they otherwise would in a normal situation.
As long as buyers are ready to pay more, there will be sellers aiming to accommodate them. If someone is selling something with a huge markup I just judge him and ignore him, but potential buyers should be warned—this, IMO, is more important.
But I vote for not hiding the price, unless there's a bunch of other things that's not relevant to the sale. (I didn't actually vote tho.) And frankly it's just much easier to trust the seller too, than someone with a heavily redacted invoice.
I'm saying this as a buyer who's out hunting for a GPU.