I think in setting the price check rules, it should be pointed out that the price checks were made as of _________. There's no guarantee a price check by a particular individual is valid, and that's always a risk, but even a person who knows prices is only correct as of the time the price check was made. The economy fluctuates quite a bit and on a regular basis.
Of course, the time of a post is always noted, on every post, but with price checks it might be best to explicitly point out in the forum rules that "freshness" is a huge issue in the price check.
Of course, the time of a post is always noted, on every post, but with price checks it might be best to explicitly point out in the forum rules that "freshness" is a huge issue in the price check.