I had one of mine on full livery some years ago. I was very naive, never having done it before.
I was paying for him to be exercised a couple of times during the week, but I always found my tack exactly as I'd left it. At first they said they always cleaned it after use - good service, I thought! - but then I started leaving the stirrups on odd holes, and guess what!
I also didn't realise how little turnout he got in the winter. He was lovely and fresh when I rode out, but then I discovered he was only going out for an hour or so a day while the boxes were done.
Bedding was skimped on; feed was sufficient but a bit hit and miss - they all got the same, but it was mixed up in a big tub and just dished out from there, so if it wasn't well mixed some would get more chaff and others would get more mix. I had no control over what he was given.
Worming was also a bit suspect; I took my own wormer along when I moved in, but found it in the cupboard several months later - they said they'd wormed him with the same as the others, but of course being suspicious about other things made me wonder if he really was being wormed as well.
I learned about some of these things when a friend started working at the stables part time, but by that time I'd moved my horse to DIY anyway.
I'm sure not all livery yards are up to dodgy practices, but you really do need to make sure you find out what's going on, call in at odd times when you aren't expected and generally don't take anything for granted until you're sure it's all above board.