I remember when I was a college kid working for a plumber as his helper in the summer. Every morning we would go to the local dinner for coffee before we got started for the day.
One morning the dinner owner came over to the table and told the guy who owned tire shop in town, who way sitting with us. I a got a special on 4 shock absorbers and my car really needs them. When can you put them on?
The owner of the tire shop said I will get back to you.
Then next day the the tire shop owner was there and when asked for his order he asked for a glass of milk and a bowl. The dinner owner came over and said what the hell is this. The tire shop owner said. I got my own corn flakes and he did!!
How many times have I told clients I won't install customer-supplied zincs? I ask them, "Would you take your car to a mechanic for a tune-up and ask him to install the spark plugs you found at Wal-Mart for cheap?"