You know the ones ...
... they always come to you with a last minute deadline and need you to produce the information NOW.
... they're either late, don't turn up or let you down at the last minute.
... they expect you to do everything for free.
While it might be hard to say no, after all, you need the business. Don't let them get away with it. If you do, they'll continue this pattern of behaviour and things won't change and could get worse.
Be accommodating and flexible but don't bend over backwards if it's not going to be appreciated. Don't put yourself out if you know they'll just take you for granted.
Yes, you meet their last minute deadline but it will cost them. Not only will this make them value their time but it might also make them avoid too many last minute deadlines in future if they know there's a financial penalty.
Yes, you appreciate things happen and sometimes people turn up late but you expect an explanation and an apology.
Be clear in your terms and conditions about lateness, cancellations, missed deadlines. Do you charge by the hour or for a project? Consider the best option for the work that you do.
Sack bad clients! Sometimes it can be worth losing a bad client that doesn't value you so that you can replace them with one who does.
There's a distinction between going the extra mile for a client, offering them great quality and value and going over the top.
Value the work that you do, value your skills and ability and don't let your customers take you for granted.