MM + Bad Key = What ?

So a concern of mine with using a MM is.. say we're trading 2 game keys for the example..

Scammer's game key is bad & they know it..

MM can't check the key without redeeming it.. so.. just has to assume it's good..

A smart scammer is going to try to blame the MM & either swear they must have used it.. or the not scammer party & the mm must be scamming them & either one of them used the key..

I'm assuming the unfortunate answer is that's a risk & not much can be done about it within such circumstances..

That about right ?

 

@Jaladhjin
You posted this in the wrong section, but I'll answer the way I would take away this risk.
I record every middleman I do. If your situation were to happen I would hold the money for the game key, let you redeem te game key and make you have proof of it (so you cant say the game key is invalid while you just redeemed it, probably screenshare) and then give the money to the game key seller if the key is redeemed. If the game key seller gives a game key that doesnt work and blames me I can post the full recording of the middleman trade to show that I did not redeem it and that the seller is lying.

My Middleman thread by the way if you need a middleman for any kind of trade
[Free] Buyacc's Middleman Service [$100+ Donor]