I’m a dog walker and cat sitter and I don’t think that the Cattery has been unreasonable- they made a booking for your cat and would have had to decline other requests for that enclosure on that date. They have finite availability and when you take some of that availability you can’t then expect to cancel without paying anything.
I visit lots of cats and IMO using a cat sitter is often a really good option. Many cats value being in their own home and I’m able to stick to their familiar routine. In general they warm to me swiftly and enjoy plenty of fuss / cuddles / playtime / whatever floats their boat. Everything is done exactly as the owner requests and on the cat’s terms. I administer meds, monitor health, clear and clean trays.
I love my job and take the responsibility very seriously. I’m pet first aid trained, and continuously study dog and cat behaviour and care. I go to great lengths to provide excellent care over and above what was asked for- additional visits if needed, continual TLC when health problems occur, added extra days due to delayed flights, nipped back to air houses when it is hot, cooked or sourced food when fussiness sets in, weighed bowls when eating slows, combed out furry knots, cleared up god awful hunting carnage, provided warm spots / dark spots/ cosy spots / whatever cat needs spots.
I’ve worked for some customers for almost 10 years. Many of the cats I care for know me really well and greet me like an old friend, happily settling down for a snooze on my knee. I know them well too- what they like and dislike, where a tickle is appreciated, which flavour food they prefer, where they like to sleep or catch some rays, if they like a tap turned on for a sneaky drink, what makes them nervous etc..
Occasionally a cat is too nervous to interact freely with me. In that case I take time to observe in detail from a comfortable distance, only interacting directly if observation alone is insufficient to be sure all is well. Almost always these cats begin to relax once they realise they are safe with me and that they can trust me to work on their terms.
To do my job well I have to limit the amount of cats which I can visit each day. This means that once I reach that limit have to turn away any additional bookings. So, like the Cattery in the OP I would be out of pocket if someone books and then cancels me. Luckily this doesn’t happen often so I don’t take a deposit, but if it became an issue I’d have no choice.