I'ma dog trainer and some clients don't want to give treats directly from their hand to reward the dog. Can placing the treat on the ground be an acceptable alternative ?

I think this is one of those case-by-case scenarios so the answer would be "that depends" It depends on the dog, the client and the behavior you are training. If they don't want to do it because the dog bites their fingers, then they need to be taught the correct way to deliver a food reward.

With that said, a food reward on the ground is better than none at all although then the dog will likely be more focused on the ground and guessing where the next reward comes from instead of staying connected with the handler.

We recently released a new course on using food, maybe it might give you some ideas for clients?