Why Does the Shop Always Find Something Else While It Is Up There?
Once a person has already committed to spending, their resistance to spending more collapses, and it happens fast. The second item appears because of: 1) the sunk cost fallacy, your car is on the lift and the labor is already bought 2) ambiguity aversion, you cannot see what he says he sees, and an unknown feels more expensive than a quote 3) the framing effect, since while we are in there is priced like a discount when it is plainly an addition. The second item is rarely urgent. It is convenient.
Why this keeps happening
The car on the lift commits you
You cannot see what he sees
While we are in there is framing
Urgency is rarely the reason
How it escalates
Ask what happens if you wait a month and listen for a real answer.