Start by removing all items from it. Then carefully look it over, in detail from top to bottom, inside and out for a name or company stamp on it. Some form of identifying mark.
You can't lug that thing all over the place, and some dealers will under price a high dollar item, so you'll sell it to them cheap.
Your best bet, and you clearly have access to the internet, is to do your best to ID it on some level, so you have a starting point. Check it out, and see if there's a name or logo on it. Let us know if you turn anything up, might be able to point you in the right direction.