Dead easy. I've done two of them, one cat and one dog, and may try to pick up a third tomorrow.
For the ones I did, you're trying to see if a certain product is mentioned and in what context. If they don't mention it (neither of mine did) then most of the questions are N/A.
If they do mention it, you need to report what they said about it (that's the only narrative required), and who told you about it (Vet, technician, cashier).
The hardest thing for me was remembering to look all over for displays of product, brochures, or posters advertising it.
If you do one of these, go about 10-20 minutes early so you can wander around the lobby noticing posters or brochures, although that backfired on me the other day when they took me right in. But there were no posters anyway.
Some of these shops have to do with whether they discourage you from trying to buy the product somewhere other than at the vet's. It depends on which scenario you do, I think there are about a half dozen different scenarios.
One of the vets I did carried the product and recommended it; the other didn't carry it at all. So you really won't know what you're going to find until you get there.
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I pray it does not occur that the last thing I did before I died was vacuum the house or eat broccoli.