Sometimes I get requests to look at people’s items and inventory and try to appraise a price (very roughly) and really it’s just a guesstimate. Usually I would use the relevant market “ticker” such as AH for Diablo 3 (though it can be towards the high side as not everything sells) or Steam Community Market for Dota 2 (if it is listed or marketable). It can be stuff like “hey! what’s the most valuable thing in my backpack?” and I try to take a look. Like any appraiser I suppose there is no perfect answer.
Other times it could be a request to build a set. Perhaps its not being sold, so one has to obtain it from another market. Other times there is one payment or mechanism that is held up and waiting a blue fix or troubleshooting, so help can be given by some sort of temporary bridging. But often this is with people around the same region (or sometimes jurisdiction if that is more appropriate) or a common/mutual circle.
If you want someone to look at your items, usually forums are a good place to start such as d2jsp for diablo 3 items. If you’re looking for dota 2 item appraisals, and your item is marketable, you may be able to try the steam market for past data. Otherwise you can try leaving a note here, and maybe someone will look at it at their discretion, but like all thing it has to be agreed that it is at best a guesstimate