Dear Mary: Why is my brother making me pay £400 for a drawing of my cat?

Q. I would welcome your advice on a tricky family matter. For my 70th birthday earlier this year my brother gave me a voucher for £100. This could be used as credit towards a drawing of my cat to be commissioned from an artist friend of his. I duly provided photos, only to learn that the £100 would represent just 20 per cent of the list price, and the balance to be paid by me would be £400. I am wondering whether my brother is doing his friend a favour at my expense — indeed in my most churlish moments I doubt whether my brother even paid £100 to his friend, and instead just negotiated a 20 per cent discount. Your prompt advice will be appreciated, particularly as the artist has completed the drawing without my go-ahead, has given it to my brother to pass on, and will therefore expect payment.
—