James
What Martin says is correct. I work for six at the moment anc had to wait six weeks for the one but as they take no commission, i don't mind. A lot of them wait until a tenant is lined up before they have work done, so don't expect a sudden influx of work to come in or a vast number of jobs handed to you on a plate.
Treat it as a bonus supply of work and don't antagonise any of them. Regarding receipts i made a receipt book with a double copy system and i write one straight away to give them when the keys are returned.
As a matter of course, i always take a digital camera asrust in some properties you will see very dirty carpets and these can be useful for your own portfolio or should you not get paid. I take all letting agency work on trust and have never not been paid. If you offer a no hassle service to them you are on to a winner.
Dave