This idea of buying and selling livings vs. giving a living to someone is obviously something that Jane Austen knew about, with her father and two of her brothers in the clergy (I think Henry was a clergyman for a time, and James was as well).

Below is a link to a long thread at L&T on the question of whether or not it was proper to sell livings. It was apparently an accepted practice and done all the time, but it does really say something about Colonel Brandon's character that he would use it as a means of trying to do good for someone, rather than for personal gain.