If your concern is 'fair market value' you can always just bid creep. Most folks put things up for the minimum they're willing to get. If i had to arbitrarily guess at a starting bid that'd ensure profit for the seller i'd think 500k for crafted crap (converter fodder), 1 mil for crafted useful but not highly sought (tstrikes, gaussians, perf shifter, e.g.), 2 mil for sought after but not premium (resist or heal sets, e.g.), 3 mil for premium. (uniques, defense, e.g.). Purples, pvps, winters and ATOs the bid history is usually a good indicator. Note these could be higher than what you might get it for if you're patient or lucky or weren't concerned with being that guy who bids 1 inf. Then just creep til you get it if you want it now or leave a bid where you feel comfortable and wait.