The egg solution is the preferred choice it's a very grey area to get into going the legal route, for a start they can dispute the charge and even claim you didn't do the job or did a poor job, with any claim evidence is crucial or it just becomes your word against theirs.
I had one 3 storey job before xmas for £30 first clean guy said he would be in, there was no answer at the door when we arrived so stupidly we did it anyway, I texted him time and time again before he responded when he did respond I received a text saying "jog on". I have quote books now where the customer signs for the quote it's just more evidence although it's just a gesture really to engage the customers loyalty by making it appear more official and professional but instead of knocking a day off work to go to court or send out letters for a debt I'd probably spend more money on and time wasted pursuing it not forgetting the stress I'd sooner protect myself better in future.