NEVER EVER USE a company or broker that buys miles. You not only can or will loose the miles you sold but the everything in your uncles account.

You can find many news articles, flyertalk post on airlines like American, United, etc closing freq flyer accounts, brokers not paying customer, etc.

You even have true cases where miles have been transfered to relative and and at the airport checkin the relative is denied a travel and accused of getting their ticket from someone who sold their freq flyer miles.

BE VERY VERY CAREFUL. TRUST NO ONE