See, this is what I can not stand. Why is it such a big deal to post what you paid? For example, if you buy a 52 Topps Mantle for $20 bucks, it doesn't mean the card isnt worth $15,000. The members that you would want to deal with would acknowledge your "steal" and pay going rate if they wanted the cards. The shady members who would expect you to sell for pennies are the ones you wouldn't want to deal with anyway.
If I make you an offer on a card and don't get a reply within 2 days, don't expect the offer to stand.