My comments about Tony having my customers was only said in jest as in reality I do vet my customers and all my work is on recommendation or repeat business. With regard to which parts I fit and what to charge depends on many variables which can only be allowed for with previous experience. As an example, Golf headlamp recently. Cheapest factor quote was £70 for a Valeo unit, TPS retail was £55 and about £44 to me, also Valeo. As far as I am aware we do not have to stick to retail prices but it's a dangerous game to charge more, unless you can really justify it. Imagine that I went for the cheapest factor unit and then quite reasonably charged the customer £80, the customer then does a quick "google" or checks ebay. They would wrongly think I was having them over.
I don't go along with the "we must fit genuine" brigade (except certain parts) but I always make my customers fully aware of what the choices are, advise but never mislead them and then let them decide.