Sorry, but I don't blame them at all. So many times we've had young people come out to the farm and when asked they explain how they've been riding since they were toddlers, w/t/c no problem, ridden green horses for "trainers", etc, etc, only to find out they had only ridden dead headed school masters a handful of times and sat on a 4 year old at a frends house once.
The last time I took someones word for it, they ended up not knowing what they were doing, not listening, accidentally giving the horse all the wrong signals, cuing for a canter, panicing and bailing(spraining ankle in the process) and then telling everyone they knew that they had been bucked off. That was them riding a very safe advanced beginner level horse in the yard.(and they had heaps of pictures on their cell phone)
It may very well be that you are a very good rider, but with the amount of people that say they are when they really are not, stables need to be safe.