I am getting rather pissed off with my job at the mo

Seem to be getting strange customers

Example 1

Just had a bloke on the phone today who bought a set of fans for a cossie from me as both his didnt work .
I tested the fans before sending them to him ( i have 3 witnesses ) and the worked perfect
He calls today saying both the fans dont work , he has had his car to an auto electrician and he says the fans are fooked

Remember , i tested them before i sent them

I tell him i tested them and they were perfect

He starts getting agressive with me saying i have ripped him off

What do i do ?? I dont want a bad reputation for the sake of £40 set of fans ,,,BUT ,, why should i change them when i 100% know they were perfect

If i give him a refund i loose out , if i dont i get a bad reputation ,,I CANT WIN.

I know its only £40 but its the principle

What do i do

Paul