Wear a t-shirt with the words violent psycho and client tend to play ball
On a more serious note unfortunately the contracting side of business is awash with people that have no intention of paying the due bills for work.
It's not just the electrical industry, all trades suffer.
Take some of the big house builders, last year they needed to drop cost and quite a few turned to the sub contractor and stated "discount your price by 15% or you won't get work". Not good if your operating profit margin was 15% or less !
As for home owner work most play ball. Having terms and conditions for work, for payment and for extras makes it very clear of expectations and tends to help retain a good business relationship.
On all works I do I hard copy quote, caveat any possible anomalies and include payment terms. Prior to work start I insist the customer sign and date over the quote paperwork which means the contract is legal and thus I have recourse should things become difficult.
The biggest issue I have tends to be extras, where say a single lamp fitting was quoted and suddenly they want downlights, wall lights and multiple switching. In those instances I print out a variation order and ask the client to sign as accepted before I do the work.
I've never been knocked, but the few that have caused issue have unfortunately always been ethnics- they will agree a price, sign for such and still attempt to extort further discounts post works.
You do tend to acquire a 6th sense for clients that are likely to become problems, hence I won't do work for builders (I quote direct to the client and offer a intro fee) and tend to be very careful when dealing with BTL landlords.