Apart from the catalogue it is essential to keep ears open in the ring as the auctioneer will frequently announce such issues not printed in the catalogue. It can be hereditary - often associated with digestive difficulty, born of boredom in a stabled environment without turnout, or copied by one horse from another. Personally, I would not buy a filly / mare that weaved. I have bought a windsucker mare - she and her offspring were the cleanest winded horses you could wish for. You can stop it with a strap / headcollar device which I did for the duration of her time with a foal until after weaning to stop the foal imitating the behaviour. Otherwise I left her to do it if she wished. Only two of her more than a dozen foals did it, both colts, and her fillies have not bred any with a stable vice as these things are termed.