I know what your saying about wrighting them off as I have done in the past....
Some people move without paying etc etc etc
It comes with the job...
But when you got a tosser like this bloke, I don't want to be taken for a fool.
Take him to court, I would, I tend to let some debts slide, but if they annoy me for any reason I sink my teeth in and will not let it go till debt is settled even if it costs £100 in cost I would still do it, they pay the costs anyway, a verbal agreement is just as good as a written one so dont let that hold you back. Go get your money 
Ian
p.s do not let them off the late payment fee, charge them an admin fee aswell, they are clearly take the P
I was cleaning the high reach windows of a shop in the local town centre. They are taking the p now and they annoyed me when I last requested paymentr because they questioned my honesty. It is now more about getting revenge for doubting my honesty than it is about the money. Sometime this week, I will be sending a 14 day warning letter by registered post (so that they can't deny receiving it). Just to show that I'm a very reasonable person, I will send a 7 day warning after that with a blank court form just to show that I intend to carry it out.
If a domestic customer were to say to me that they had fallen on hard times and were genuinely unable to pay I would just say to pay me when you can. But take the p or question my honesty and I'll take them to court even if it ends up costing me more than the debt itself.
The daft thing is that I have several friends who sometimes buy clothes there (and I have done so occasionally myself) and if they don't pay me, it will also cost them some profit too. No way will I buy from a shop that has turned me over for my money. This is a vast improvement because there was a time when I would have not confined myself to legal retribution. Thankfully, I started growing up eventually.