He Doesn't Have the Right Part
If you have a plumbing repair you need tackled, then you want it finished as soon as possible. This is especially true if it involves the toilet or any other part of the sewage situation at your house. The last thing you want to hear from your plumber is that he's going to have to wait a week or more for a specific part to become available. You'd think that with a plumbing truck full of parts this would never be the case, but it is. Let's say your house has been renovated, but still has some of that 90-year-old plumbing under the house. This could present a parts problem, or it may lead to a larger repair than you anticipated. Either way, this is the kind of conversation your plumber knows you won't enjoy having.