In my experience, this doesn't happen often. Most of the time, the check-in clerk will either accept the $0 rate without questioning it, or they may question the rate simply because they don't understand how you got it! This was the case with my last BRG at the Quality Inn in Temecula, CA. My free night was accepted, but the female clerk seemed confused. She said: "I see you had some trouble at the (nearby) Comfort Inn and they sent you to us".. (Huh?) My response to her was: "Uhhh .. yes ma'am!" (I would've agreed with anything to have avoided a problematic check-in!) Going along with her understanding of it seemed much easier than telling her how I really received the complimentary night!
Most often, that's the type of "awkward" scenario that you may experience. However, once in awhile you may encounter a belligerent manger or clerk who will do his or her best to make you feel like you're cheating the system. They will tell you: "somebody's got to pay!" This is when the fun part starts for me .. the time when I feel compelled to explain to these guys how the ChoiceHotels.com "Best Rate Guarantee" works! (Shouldn't these folks already know this stuff?) If I were them, I would feel mighty embarrassed that a customer has to explain to me how my own BRG works. The satisfying part of this is that I come out looking more knowledgeable than they do! Sad .. really sad!
There are times when you may have to comply with their demands for payment. Don't worry though. While the situation may seem hopeless, you will be reimbursed by Choice. Don't just walk away thinking that you've lost the fight. You've been assured (from the guys at the top) that the night is indeed free. And that is what it will ultimately be. Demand a receipt though, if you find yourself paying! A resolution to this problem will eventually work in your favor.
If you find yourself pleading your case with the hotel clerk at check-in, there are still a few options you can try before "giving in" with payment. First, call the Choice Hotels customer relations department at 1-800-300-8800 and explain the situation you are having with the hotel (they are available during regular business hours, so call back in the morning if it's late). Once you get in touch with them, follow their advice. They may even speak with the clerk or manager directly. You may also want to call the "BIRG" department directly @ 1-866-633-4100. If you wish to try them first, that's okay too.
Hopefully, you have brought with you copies of your approval letter and reservation details - just in case they wish to make a photocopy for their records (you can keep the originals). Usually, with non-eventful check-ins, you won't be asked for any documentation, but always have it handy in case things do not go as planned. Whatever happens, be pleasant (bite your upper lip if you must). The room is free and you wouldn't want the hotel to stick you with a "lemon" to spend the night in!
Hope this helps.