amazingtrade said:
I either have to change things, get laywers to draw up policies etc and move on or get a 9-5 and I hate 9-5

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You don't need a lawyer to draw up your procedures or agreements. You need to sit down and document:
- title of the service you are defining
- definition of the service
- what are the included deliverables
- what is excluded (here you might want to detail caveats regards WiFi and houses)
- what is required from the client to enable delivery (access to the site, light, power, etc.)
- what is the definition of completion
- what are the terms of the agreement (the parties involved, start date/time and end date/time, applicable law, payment, etc.)
- what is the procedure for reporting problems after service has been delivered and what is the expected response (here you may want to refer to a separate document which highlights typical WiFi problems).
- what is the remedy procedure for problems - this is the section where if the warranty on devices/products becomes the responsibility of the manufacturer, that you describe this fact. Ie. you installed my router and now it doesnt work: you define that you will attend to check the setup but if the router is dead that they must contact <netgear> regards warranty fulfilment.
- some other stuff
- signatures
This migh be OTT and you might just want to take the obvious bits, but the above is, in basic terms, what our clients have to sign and return at least 48 hours before we will visit their site.
I realise agreement in advance would probably be v difficult for you and might make doing your kind of work impossible, so I would say you need them to read and sign the agreement (make it as friendly as possible) at the point you arrive. If they can't agree then you have to decide whether you're prepared to take the risk of doing the work.