We have a few pets and have had people watch them successfully many times, we have also watched over peoples.
In the 16 years we have been married and doing this we have only ever had two incidences:
We had an old cat and asked a neighbour to feed it for a week. The cat mostly lived outside anyway so we asked them just to leave food an water on our back step each day. All was going well until the neighbour came around half way through the holiday to find the cat dead on the door step. hardly his fault as we had been waiting for that event for some time, just unfortunate timing.
The other incident was shortly after we married, at the time we lived in a flat and our only pet was a hamster. Before going on holiday we dropped it off with my wifes 8 year old brother to watch for two weeks. He took excellent care of it and was very diligent (according to the MIL). We arrived back two weeks later until all is well, it was a nice day and we were talking in the back Garden. Wifes brother brings the hamster out to see her, slips on the back step, and drops the hamster how quickly darts under the shed. After ages of trying to coax the little animal out we almost gave up hope, we were discussing alternative when the cat tunrs up, dead hamster in mouth....
Sill two incidents in all those years is not bad...and we have had plenty mare 'bad' incidents whilst we have been in charge...
...Good luck and if something bad does happen, don't try to cover it up, just own up!