My Dad often offers to get one of his friends to do work in our house -fit the bathroom, change the taps, replace radiators, etc. I let him arrange it because we've never been close and it's his main contact with me (long story).
However, my experience is that it's much more stressful when your mates (qualified plumber, etc) do jobs for you. We seem to always end up in a situation where we are not being treated like customers - not given a date that they will do the job, and just left waiting around for ages for when they can 'squeeze us in' between other jobs.
BTW I don't think he gives us a particularly cheaper quote as it seems in line with what I expect / have researched.
Also I am often persuaded to let them choose fittings for me. At the moment they are making it very difficult for me to pick my own kitchen tap, for example - warning me I will pick a rubbish one. I have to have one they pick. My bathroom had to be chosen from a particular supplier that did not have a showroom or website, and I had to pick from a blurred on-line catalogue (when the sink arrived I disliked it and would never have picked it in a showroom, but they'd already fitted it so it was too late).
Is this normal, to have tradesmen pick stuff for you or make you use particular suppliers? They make it very difficult for me to do otherwise.
I have now fallen out with my Dad over this, as it's caused some tension. I'm thinking about just organising it ourselves in future.