In reply to Will_Thomas_Harris:
ABE books is a good source to see what sort of prices are being asked for a particular book; you can filter by signed copies, first edition etc. Currently there are about 30 signed Rebuffat's ranging from £30 to £350 although the majority are French editions.
I use ABE to value my collection for insurance replacement purposes.
If you book appears to be being offered for say an average of £100, no dealer will offer you anything like this, so prepare to be offered say £40.
Once you have some idea of value you may well realise more money by advertising on UKC or eBay. At least you will know if a dealer is taking the piss with any offer they make.
Condition is very important, Jarvis is quite a stickler and may well want to examine them in the flesh before making an offer (quite reasonably)