I doubt Ben has resource guarding if he just lets you trade. It's not the same thing to just steal something and be ok with trading, and stealing it and growling as soon as someone gets close. He never guards his own stuff, just the random clothes/washcloths/papers he picked from the floor. Probably because he knows we used to react strongly when he did that, so he gets defensive knowing we will want it back.
The only thing that works to get it back is throwing bread away from him and he eventually leaves the object to get it. Now, if you're relax about it and pretty much ignore it, he won't growl as soon as you get close, but you still won't be able to get it back (although eventually he leaves it if you ignored him long enough, but by then the thing is destroyed). We always managed to get the low value items back by trading, but it never changed anything with the high.
It wouldn't have been so bad, except he stole everything. Couldn't leave laundry on the bed, toilet paper in reach, papers on the floor, baby toys on the floor... I swear I spent more time monitoring him and trying to get the stuff back than doing anything else. Most days I just let him have whatever he had all day so I didn't have to bother with it anymore, but then he spent most of the day in his crate... You have no idea how relaxing the last few days have been... I was able to leave the laundry basket in the bedroom, then leave laundry on the bed there... I can leave the toilet paper wherever I want to... I don't have to worry about leaving paper too close to the edge of the table... I don't have to put the kids' toys in the play area every time they throw one out... it's huge. It probably doesn't seem much but when you're trying to put a kid's meal together when the kids are screaming, not having to take those 10 necessary steps to make sure everything and everyone is safe is a big deal.
But yeah... it might be different in another environment. If he's more active and is clueless about how people react to him stealing, he might not react the same way when he does, or might not steal at all, if things lose their value because he's more stimulated. It's what I'm hoping at least.
