I don't have a dog that's grabby with treats, but I'll tell you about a method that I've heard works for this problem.

First though I'll let you know why dogs with this problem seem to get worse quickly.
Someone gives the dog a treat and he entusiastically grabs a finger. They give him another treat and same thing...well that happens enough and the person giving the treat becomes hesitant about giving it. Afterall they like their fingers. So they caution "beeee niiiice..." and slowly bring the treat down. The dog makes a move forward and the person pulls the treat back to prevent their fingers from being chewed. The person puts the treat down and the dog lunges forward even more excitedly, so the person pulls back the treat again. By this time the dog is so worked up because it can see.smell the treat but is being teased with it. It is hard at this point to get the dog to settle down enough to take the treat.

So the solution I have heard of is to take your hand and push it into the dogs mouth quickly. The dog does not want to eat your hand, he just gets too excited, so he will back off to get your yucky hand out of it's mouth at which point you can open your hand and release the treat. Your hand is really close to the dog's mouth so there is no need for it to lunge for the treat. it should only take a few sessions of spitting out your hand before your dog learns to back off until the treat is within taking distance. You can also put a command to it, like easy or be nice or gentle.

Another way to train that command is to hold the treat in a closed fist and let the dog sniff it, but not get it. The moment the dog backs off you open the hand and give the dog the treat.

You can also do that with clicker training.

Whatever you decide, good luck!