I use "Coachies", tiny heart-shaped treats that are natural with no added nasties. They are incredibly small, but Tilly would do anything for them. I buy them from my local petshop and I think they are quite easily available.
You should find that your trainer is quite happy for you to train Beatle using toys for a reward rather than edible treats. I was told by a police dog-handler that her drug-sniffer springer was trained with a game with his ball as a reward, rather than something edible. As soon as Frank found something he was immediately given the ball for a few minutes. Of course, it is important to teach the "give" command if you want to train for more than one exercise during a session

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I wouldn't worry about Beatle not responding to treats, some dogs just aren't food orientated.
Like Harv, Tilly has to know there is something edible for her before she will agree to do what I want her to

sue and Tilly