<human>: Can you provide a brief rundown of the text in within 3 sentences?

Hiya,
The dog I'm going to be adopting, [Blue] is clearly not used to wearing a collar, therefore whenever I do reach for it he'll flip over and mouth me off. I work at the shelter he's at so it gives me some time to work with him before I finalize the adoption, so I'm also working on him with leash biting. My co-worker told me simply to grab his collar and sit him down when he starts leash biting and give him a stern 'No' and reward him when he calms down but typically whenever I reach for his collar or even his side he growls. I can't really tell if it's a 'warning' or a 'playful' growl and I don't want to misinterpret what he's telling me. I tried him in a harness to see if he's any better but after a few minutes he kept somersaulting until half the harness was in his mouth and i still couldn't reach for his collar or the harness without him growling. 

Normally I would keep at trying to reward him when he calms down but once he's outside he doesn't really show any interest in treats, unlike when he's inside he can't get enough of them. And what I'm mainly worried about it not necessarily him biting me, but if he manages to wiggle out of his collar at some point and I can't grab him without him flipping all over. 

If anyone has any advice on how to work with Blue on getting used to wearing a collar having it used, or a harness I'd really appreciate it. Or any really smelly treats that might get his attention better to reward him for good behavior.
<bot>: Shelter dog doesn't like his collar grabbed and will flip and possibly will growl when i do so, not sure if playful or a warning. (growling typically accompanied with leash biting)