Ask H&H: how can I prove a seller is a horse dealer?

VAT second-hand margin scheme, Exchanging money, buying a horse, sales, deals, sold, twenty pound notes
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(Image credit: Horse & Hound Stock Archive)

Q: I purchased a £2,500 horse without a pre-purchase vetting. It has turned out to have severe rotation of the pedal bone. I wish to take out a small claim against the vendor, who says she is a private seller and not a dealer. I have downloaded more than 10 of her adverts for horses over the course of the past year, but what is the definition of a horse dealer? My court case hinges on proving that she is a horse dealer, as obviously I have more rights.

JJ, Kent