] Why did the death of the incumbent matter? If the right of presentation was the patron's property, why wasn't it freely transferable at any time?

The right of presentation, or, more correctly, the advowson of the property was an inherited right that couild be legally passed on to another party. The right consisted of being allowed to propose a candidate for a living, not the right to install one. The right to actually install was the perogative of the local bishop. This is important , because it does mean that a holder of the advowson couldn't arbitrarily hire and fire a parson . It's also important to reember that a parson was hired for life, or until he chose to retire. Therfore, the vacancy could only officially occur when the incumbent died. Officially, there was nothing to sell, and the selling of livings should not have happened. However, competition for livings was fierce, and some prospective parsons were willing to enter into a contract to be the next in line for an exchange of money. They literally bought the aprroval of the owner of the advowson...and we see that happing in MP. Although it wasn't strictly illegal, it was considered rather disgraceful, and it's obvious in MP that Sir Thomas would not have done it if he hadn't needed the money in a hurry.

How was the right of next presentation valued?

When a parson died or retired, the church auhtorities made an official inventory of the living and assessed its value- a rather arbitrary and inexact science, but simple to operate. I presume Robert is talking about standard selling practices in teh book; I have nothing to add to that.

Was there a regular market in next presentations, as there was in Parliamentary rotten boroughs?

Neither were officially approved,so I don't know how "regular" you can claim either to be. Both livings an dprosepective incumbents turn up in newspapaer ads for the time, however- James Austen advertised himself in a spoof one in his Oxford magazine.

How was the sale and purchase of next presentations perceived by members of the upper classes less mercenary than RD? Was this a respectable way to acquire patronage on behalf of a younger son or a nephew?

It was done. However, doing it before the incumbent was out and done with always seems to have been a bit shady. I don't think JA herself approved of it, and it certainly was one of the complaints about the church system that got addressed pretty rapidly after the wars with France ended- although there was not real change until the 1830's, on this, and many other matters.

Jack, have you read Jane Austen and the Clergy by Irene Collins? The paperback version is now out. It's a superb book for thinknig abotu these kinds of questions,and we are toying with the idea of making it a group read....