Agree with what's already been said. Also
What arrangements do you have for emergency veterinary care - not just what vets you go to but how do you get there, especially if the boarder doesn't drive...and if that's the case, who pays for the taxi?
As well as general info about disinfecting etc, how do you clean indoor accommodation between guests (especially if they are allowed free range time on carpet etc) or outdoor runs.
Do you board other types of animals, if so what and where are they kept in relation to the rabbits. Do you ever board ferrets. Are they kept in the same hutches.
Do you have any of your own animals in the household? If so what are they, and do they have opportunity to get near the boarders (e.g. dogs/cats in the garden).
What insurance do you have?
The most vital thing I think is to go and look before you book, even if it's a long way away. It's really easy to make websites look flashy and lovely and to be able to say all the right things, but you 100% need to see it yourself to decide whether or not you'd be happy to leave your babies there. Otherwise you risk turning up and finding that things are not what you thought. Then what? Cancel your holiday or leave your pets somewhere you're unhappy with?
It's also worth noting that as of 1 March this year, website advertising has become covered by the Advertising Standards Authority so if anyone visits anywhere which they feel is advertised in a misleading way online, you can complain to the ASA about it