Well had a site visit from our builder and plumber and electrician come around to quote us for an extenstion. I asked the sparky out of interest how much he would charge for a pdl plug price was 13 plus their markup so around 16 bucks per plug. I asked if I could provide my own plugs as I can get them online often for around 14 per plug. I was told that he would charge more labour due to the warranty falling on him if I used plugs that I have purchased myself. Is this normal Practice?