I call that a cost of doing business. And the guest was up front with you that a blockage had occurred. When I woud charge a guest for "damages" is when they flush something I've told them is not permissible, and I warn them up front that if they do, they will be charged for the repair - so there are no surprises at the end of the day. For me, when something forbidden gets flushed and creates a blockage, I can get the "evidence" out and hand it over to them. Nothing just pushes through past my pumps. If you found something had been flushed that wasn't supposed to be flushed and was able to prove what it was (by having the object pulled back out), then I think you would have an argument in your favor for charging for the repair.
Sometimes, toilet paper just cloggs when used in a large quantity. It happens on my vacuflush occasionally. I let it sit and break down for a few hours, shut off the water and then try to flush and trigger the vacuum pump until is sucks it through. But an "object" gets stuck in the first duckbill and I can open that and pull it out. Objects never flush through! So it is possible that your clog was paper, especially if you use something thick and plush like Charmin.
Not that any of you would have this problem, but how timely of a subject...Just this weekend, I got a clog - it's the calcium build up in the discharge hose - pee and salt water turn into a concrete-like substance and eventually clogs. I have to now take the hose off, go outside and beat the snot out of it on the dock to break up the "concrete" in side. About every 2 to 3 years this happens - I knew it was coming. I could hear the pump beginning to labor all week. At least it was my toilet and not a guest toilet. Not looking forward to that! This is why I've been switching over to fresh water toilets.