Marc I was just correcting an inaccuracy from someone who obviously has given you wrong info.
There is a multi tier system like probably anywhere else.....BUT a paid gig is a paid gig....Most people here do paid gigs without tip jars and the only folk who make tips or rely on them are open air buskers who hang about the city centres..OKAY some folk may busk and do paid gigs as well BUT I have never heard of anyone who works in pubs and clubs putting up a tip jar....it just does not happen.
Just for info I work through several agents who have the large corporate gigs, clubs, holiday centres, hotels and larger pubs virtually sewn up so most acts have to use them to work these establishments. There are a ton of small pubs and a few small clubs who do not use agents and they employ acts usually through word of mouth. I sometimes work that way and also get work from people who I have known for years who book me privately. But none of those gigs works a tip system. Some top acts will hire a theatre or large hall sell tickets and put on a show themselves but again no tip jar. Now I do not know who gives you this info but you can tell them from me that they have it all wrong. I work Scotland and the North of England and have done for years and tips have never happened. Remember I do not live in Nashville and your rules do not apply here. We are not a closed shop and people WILL get work if they are good enough.
Sadly things are not as good as they used to be and I am working places I would never have years ago.....many reasons for that but there is some work if you are good enough. I just had an agent on the phone only yesterday and he filled up most of my DIARY for the next few months......not enough to make as good a living as I used to but its..... OK.

http://www.soundclick.com/bands/songInfo.cfm?bandID=687727&songID=5238055