Well if they are short staffed and they know that you are on holidays then its not surprising or unreasonable that they ask you if you want to work the extra hours. Its possible that they thought of you first because they thought you'd appriciate the extra money, given that's why you've taken the extra shifts on in the first place.

If you aren't contracted to work the hours then you don't have to do them. Whether they think any less of you or not depends on how you delivered the refusal. You apologised and you had other plans, so they'd have no reason to get annoyed. They can't expect you to drop everything. However like i said before its not unreasonable for them to at least ask you. I don't think I've worked in any part time job where i haven't been asked to cover at least once

Working in a Supermarket myself I sometimes have to phone around to get people to cover shifts when someone calls in sick etc.

One of the rules I use is that I *never* phone anyone that is on holiday. Usually I phone people I know want the extra shifts and if people say they don't want to do the shifts then thats fair enough. I don't think any less of people if they won't do a shift for me however I'm pretty good at sweet-talking them into it

If someone won't do a shift for me when I phone them though then I'm less likely to phone them next time and also I'd be less likely to offer them any overtime if they asked for it..it's all about give & take at the end of the day.

I volounteered to work saturday as overtime - but then i get £14 per hour so will help towards paying all the bills for the meets lately!!!!!!!