First I have to say it is highly unlikely your dogs picked up fleas from the groomer.
I have never known a groomer that did not take precautions against having flea infestations in their salons. In the grooming world, a dog going home with fleas would be as awful as finding cockroaches on your dinner plate at a restaurant.
Your best way is to prevent infestation and to be very proactive when dealing with them. You want to go over them everyday. If you happen to see a flea or two, pick them off and dispose of them. If you see a flea or two the next day, you need to find the source and treat it or avoid going there. Did they go for a walk? A visit to the park?
Fleas come from somewhere. Your first step is finding it and stopping it there. If they have only been in their yard, then you need to treat the yard right away. If they went for a walk or to the park, you can either stop going there or go over them thoroughly when you get home.
I've never used the Flea Treats though I've heard great things about them. They are an edible treat that you give every day I think. I don't know what's in them or how they work.
If you don't go after what you want, you'll never have it. If you don't ask, the answer is always no. If you don't step forward, you're always in the same place.