I know this is probably a tall order, and I dont write code so I am probably asking for something that is harder than I can imagine to be done but....
Wouldn't it be cool if the market place wasn't just a forum, but like a listing? For example, while putting your item for sale, you have to fill in fields for what it is (firearm, optic, magazine, etc...) then fields for caliber, make, model, price, etc. Then the marketplace could retain its firearm, firearm accesories, and non-firearm related divisions, and say you click on firearms, you would be directed to all the listings with the options of filtering results by make, caliber, model, price, etc (all the fields that the lister had to fill in). Then some kind of search engine where you could type in what you are looking for and BOOM, you find exactly what you need.
I know its probably asking for more than can be done, but if it could be done, wow, the market place would be much more efficient. Hell, I would pay a buck everytime I bought something just to be able to use a system like that (and that could cover development fees, and extra $ could go to CGN foundation)