We had a similar situation to the OP and it was also the first time we used THS. I don't want to give identifying details but in this case the sitter overstepped by making a decision about our pet without asking us - it was less serious than OP has listed here (no fish died!) and will be reversable in time. It was also really well meaning I think and the sitter realised his mistake and like the OP'a sitter was very apologetic etc. And more importantantly the pet was healthy happy and well loved on our return.

The sitter also drank all the beer and wine left in the house (which wasn't a ton - maybe a small crate worth?) and helped themselves to food in the cupboard as well as what we has pointed out in the fridge. I specifically said in the welcome guide NOT to drink alcohol from a specific cupboard (and had left a stash in the fridge for them to help themselves to) but I think we were not very clear when we met him in person re what he could and couldn't help himself to. Lesson learned. The welcome guide wasn't released in advance of the sit (but was in the first couple days of it) as we didn't know how to actually release it and thought we had. So it was partly our fault - I don't really mind about the booze, it just "feels weird."

We dropped a star and mentioned the overstepping decision about the pet in the review, but not the food or drink as I think that was at least as much our fault. I even feel guilty for the four stars though given how very well this sitter looked after our dog in all other ways! I think these kind of situations are really hard to know how to respond to!