My methodology for a full re-wire.
Survey and chat with client- 1/2 day
Draw up plans showing all works- list out a BoQ, work out hours and material cost- 1/2 day.
(a non scale visio with all points, sockets and switch locations, water and gas and CU positions- it doesn't take long and it kills off nearly all ambiguity)
Submit quote and indicate terms and any caveats.
Accepted quote- move forward negotiations regarding start date, access issues and working hours, confirm continuity of work or agree stages of work.
Confirm payment method, dates, terms etc.
On a decent 4 bed I expect 100% of payment for all materials on the bulk order
20% of labour total cost within 7 days invoice weekly for a 4 week job.
The final 20% due post completion and on handover of site records and cert.
I would add that since I never want to VAT register about 75% of clients pay my suppliers bills direct. When this happens I simply add on some time for handling the material order.
A good sparks shouldn't need money up front, even if they do NEVER give any trader more than you get back.
So if he delivers £1000 of materials give him the £1000 immediately- If he gives you an invoice for 50% of the total job labour, make payment when they have done 60-80% of the job.
Over paying or payment up front can create a moral issue with some. (there morals disappear and so do they
)