OK - Performance for one has a 100% return policy in my experience. I don't believe they'd care if you actually used the helmet.

That said, I wonder if you're over thinking a helmet. Either it fits or it doesnt, either you like the looks or you don't, and ventilation should be obvious by either looking at the helmet or just comparing it to others. I think the decision can be made in front of a mirror. Maybe I'm odd, but I've never had a problem with a helmet that only showed itself after X (an hour? two hours? six hours? whatever). If it fits, it is fine indefinitely. You may be different.

Rudy's guarantee is highly misleading, I'd even say deceptive, though. In fact it's BS - it is in no way shape or form a 90 day 100% satisfaction guarantee, as shown by the small print and the comments you received from the company.They shouldn't try to make out like it is.