Just be up front with them. "Hey I'm not ready to buy right now, but you have such a bigger selection of boots than I have access to try at home. Would you mind if tried these on in size 27M to see if they'd work for me?" Of course, it helps if you have an armful of schwag from their store, and don't tie them up with several pairs of boots. I don't see the problem with a quick fit test or two. Who knows, he might find the perfect ones and whip out his credit card.