My dad is baffled by this situation, so I offered him the wisdom of mumsnet and he accepted!
His longtime female friend owes him some money (300 euros) for expenses incurred on a trip they took together. My mum went too so nothing like that. He paid for everything at the time just keep things simple. He then let her know what her share was; the 300 euros. She sent him a check for 500 euros, saying the extra was for 'all your work and help for me over the last couple of years'. He was shocked by this, he explained to me that it just seemed completely wrong, and replied he couldn't possibly accept a tip and had teared up the cheque, although he would have said it more gently than that I think. He thought that would be the end of it, but she replied back saying he hadn't read it properly, it was not a tip, to lighten up, and accept it. She said she wouldn't be sending him the money she owes him until he gave her the green light for the full amount, 500 euros. They are both wealthy which I suppose is relevant in this situation.
After some general chitchat and making other plans in his latest email, he addressed the issue as follows:
'have had a think about your 200 euros. I appreciate the sentiment behind the gift, as an expression of your gratitude for my efforts over the last few years. I understand that. And whether the 200 euros is in my bank account or your bank account makes no difference to you or to me. So it should be easy for me to accept the money as a gesture of gratitude. But I am finding it isn't easy at all. If I did accept it I fear I would feel differently whenever I helped you in the future, by planning our bike trips for example. I would have to keep saying "And I don't expect to be paid for this" . When I help you I enjoy your gratitude and enjoyment.'
Is he being unreasonable?