And for luck?

My laconic Grandfather, William Haydn Howell, (top right), was old school Welsh. My dad told a tale of them visiting a farm down west, where the owner was just about scraping a living. After choosing & crating up a batch of chickens, Haydn beat the guy down to the lowest price he could. They shook hands on the deal, and then he held out his hand, palm up, and said "for luck"? The farmer then had to give Haydn back some of his hard earned cash. Apparently it was an old Welsh tradition. I can't find anything about this on the web, but the farmer seemed to know of it.