Back in 2014 when we got our cocker spaniel, the prices were different - £650. We paid £50 in cash when we viewed her and £600 in cash when we collected her. All seemed reasonable. (The dog is good and well, just had a good chase with another dog, despite her age, and the breeder is still in business. So wanting cash on the day is not a sign of something shady). The previewing fee is a new thing, but it might have evolved in recent years as demand shot up in covid times.
There are quite a few cavapoos out there, I hear about a cavapoo here and there and it’s not like they have such multiple issues that they all drop dead in the first year. My builder just yesterday showed me photos of his 8 year old Cavashon (Cavalier x Bichon Frise), alive and strong, no issues. And I had a poodle who lived till the age of 13.
I think there is an element of panic, but if you have completely gone off the dog and breeder, you might lose the £200. It’s more difficult to sell puppies past 8-11 weeks, there are socialisation windows and things like that, so breeders need to line up buyers ideally and if you have people deciding between various breeders until the last moment, breeders need to find other buyers super quickly. It’s a very time-sensitive industry, you cannot leave puppies on shelves indefinitely:-) So there are these various reserve fees as a result. If the £200 is refundable, ask her to refund. After all, you paid it early in the puppy’s life, so the breeder has a lot of time still. If not refundable, raise it with the bank as a chargeback, but it’s in the bank’s discretion.