I think if you stay flexible and not say "I'd never put spot-on flea poison on my dog!"... but say... "if you require it, I'll consider it", and/or add that you "take measures to make sure fleas & tics are taken care of"... and then do what you think is best for the dog in question, anyway... you'll get further.
We don't do regular flea & tic meds, but I do conform to the requirements where Denna boards. She took Bravecto for the first time ever a few weeks ago. I minimize exposure where I can. We're cold enough that heartworm is not a problem, so she doesn't get that med (I did have Denna tested last month, just to be sure, and she's clean).
Our current house has never had a flea problem. We brought some home from a relative's house one holiday many years ago (pre-Denna), and did dose everybody with spot-on treatments, did lots of laundry and powered the bedding... once.
When we travel, I've started using essential oil "spot-on" flea repellents. I don't think they work to stop an infestation, but so far, we still haven't had a problem. Some of the ones based on cedar oil say they kill fleas, not just repel, too.
We have adopted two dogs via rescue. We must have told a good story (and/or they recognized us as serious dog-lovers), because we didn't have any troubles.
Let us know how it goes - and bring PICTURES!
I follow a senior rescue, "Old Dog Haven"... and am contemplating providing foster care... just haven't got up the gumption yet (and business travel keeps making me think twice about how/if I could make it work).