Don't know about airsoft, but I am familiar with standard pricing for used airguns.
The general rule is 66% of new price if the gun is in mint or excellent condition without scratches or marks. Less for guns that bear the marks of use.
Of course many people disregard this rule and try to sell their stuff for 30 or forty quid less than they paid for it. They are rarely successful. Most buyers would prefer to pay the extra 40 quid for a brand new guaranteed item. And some sellers use terms like "excellent" and "mint" in a very cavalier way.
Anyone buying a used gun is taking a risk. There are plenty of wide boys out there selling stuff. And this should be taken into account when it comes to pricing. I have always stuck to the rule, and lost money as a result. However my guns have always sold quickly.
