Jim said, 'The salesman was very nice ...

[vectra]

Hello,
A very happy New Year to you all,

A few days ago my students did a series of tests preparing for an upcoming exam. One of the sentences they had to put into indirect speech was :
Jim said, 'The salesman was very nice when we bought the car.'

We changed the sentence like this:
Jim said the salesman had been very nice when we - and here comes the biggest question - had bought or bought the car.
I think had bought is the right option.
Is it so?

Thank you in advance for your time and help on such a busy day.

[apex2000]

Just 'bought' is correct.
If you say 'had bought' it implies that the salesman had only been nice after the sale.

[dnguha]

I would go with apex2000.
The past perfect tense is used to talk about an action that took place in the past before something else took place. One more example is given to support the argument.
.Direct speech :- Tom said, " She just made some coffee when I arrived."
Indirect speech:- Tom said that she had just made some coffee when he had arrived. ( It is not correct interpretation)
Tom said that she had just made some coffee when he arrived. ( Correct)