100% don't need to pay for the sink.
Remain cordial but make sure its always clear in any correspondence that the change was due to it not being possible to fit the other sink (as advised by him).
Don't mention to him the possession of the unused sink as in the (likely impossible) scenario that he does take you to court then the fact that he retained possession would be a massive final nail on the day, in the coffin he's already put himself in!
Chances are that nothing more will come of it and I'd think even bothering with letters chasing the money and threatening court action would be too much effort for £65.
If you do recieve any letters I'd advise a short and to the point response in writing allong the lines of 'The sink in question was specified and supplied by you. As you were unable to fit the sink, I was unable to take delivery of it and as such it remains your property.
Because of this I will not be paying for this item and altho you are free to persue this matter as you see fit, you should consider this my final and only response regarding this issue (short of seeing you in court).
Any continued correspondence regarding this will be considered to be harassment and I will be persuing legal action of my own.
Regards ________ '
Respond to any other letters with just 'please refer to my letter dated____'
Remain cordial but make sure its always clear in any correspondence that the change was due to it not being possible to fit the other sink (as advised by him).
Don't mention to him the possession of the unused sink as in the (likely impossible) scenario that he does take you to court then the fact that he retained possession would be a massive final nail on the day, in the coffin he's already put himself in!
Chances are that nothing more will come of it and I'd think even bothering with letters chasing the money and threatening court action would be too much effort for £65.
If you do recieve any letters I'd advise a short and to the point response in writing allong the lines of 'The sink in question was specified and supplied by you. As you were unable to fit the sink, I was unable to take delivery of it and as such it remains your property.
Because of this I will not be paying for this item and altho you are free to persue this matter as you see fit, you should consider this my final and only response regarding this issue (short of seeing you in court).
Any continued correspondence regarding this will be considered to be harassment and I will be persuing legal action of my own.
Regards ________ '
Respond to any other letters with just 'please refer to my letter dated____'