I'll try to be brief! My teenage DD approached a family-run restaurant that was looking for waiting staff and was told that she should come in for an unpaid trial and they would let her know. She did, they called her after and offered her a shift, she turned up for it and was told after three hours, when the rush was over, "Oh, this is another trial, unpaid, you can go home now." She wasn't happy but was desperate to land her first job, so when they offered her another shift, which she confirmed would be paid, she went in and again was told to go home after a couple of hours as the boss's son had turned up and wanted to work. 
Then, for three weeks, they didn't call her in for another shift, just kept telling her they had no work. A friend told her of a job going at a place she was working in and she got it, did three shifts last weekend. The old place owe her 20 pounds and didn't pay it into her account, instead they told her to come into work tomorrow (an hours journey by public transport) to pick it up and have a meeting with them. They have a track record for being unpleasant as bosses, which she knew before she applied for the job, but she said she would ignore it if it meant getting her first job. Now she is scared they are going to get nasty with her and wants me to come with her. They haven't a bloody leg to stand on with her as far as I am concerned and I think she should just go in and face them and tell them, calmly, that yes, after being left high and dry by them and treated fairly shabbily, she has found another job. She has to learn to be an adult and do things without me at her side. But she is worried sick about tomorrow - should I offer to stand outside the restaurant and go in if she calls me on the mobile to back her up? She is only a kid and these people love to power trip, which is why they are demanding she do a 2 hour round trip for twenty bloody quid! I'll be honest, part of me wants to walk in like Clint Eastwood and demand her money on her behalf! I am driving her in partially because I can do some shopping in the town, partially because I don't want to give these arse holes the satisfaction of wasting her whole morning when she is meant to be revising for exams!