I know that while many gallerists are kind and honest folk, there is a small minority that gives the trade a bad name by devious practices.
Stories have been reaching me of an artist who has done well both locally and nationally. He showed some pictures with a gallery at a recent art fair where they sold very well. The gallery wanted more, but for whatever reason, they were unable to get the artist himself to supply them, so they went online and bought some from a website. The pictures they'd bought did not do well, however. In fact, they didn't sell at all.
When it came time for them to pay the artist, they did something I still find quite astonishing: they gave him back the recently acquired paintings, deducting their cost from what they owed him, and then factored in the cost of VAT and told him he owed them for that!