You say that it's quite common for people to get their own products and ask for a proffesional fitting service, so when you're quoting for a job where you are using a customer sourced product why do you not check for things like this?
What like you buying the wrong fire?
What are we mind readers?
How do you price for someone buying the wrong stuff,do we simply add on another £200 or what just in case it is wrong?
Is that proffesional(sic)?