All a question of bike/Ducati experience.
The 748R is not an easy bike to get on with, so an owner has to be willing to compromise allround rider friendliness for the full on focus and consequent feel of a 748R.
It is, as I'm sure you already know, Ducati's homologation entry for the Supersport class and as such certain aspects have had to be present on the street bike in order that they may also qualify for use on the race bike in accordance with the strict race formula. Couple this with the need to meet strict emmission controls (for the street model) and also to be at a price that ensures enough of them are purchased, at street level, so that they meet the homolgation quantities necessary. You can appreciate then that it is no easy task getting a race designed bike fit for the road, as you will find out if you get one.
The fuelling will need to be sorted out, it's not perfect for every occasion.
The slipper clutch fitted is also not the best on the market, but once again a compromise.
The standard suspension settings are too hard for normal road use, they will need tweaking/changing.
If you're still going for an R get the best your money can buy. It should be immaculate-
full Ducati/independant specialist service history-
low mileage is not an absolute gauge that the bike has had a good life, so don't be scared of higher mileage -
question owner on warming up/riding/maintanance habits, a bike that has done lots of time warm running is infinately better than one where it has had little use and most of that cold-
avoid ex race bikes
If this is your first Ducati, may I suggest a test ride on a 748S first and then ride the R, see which one suits your riding style better for now, you can always upgrade later.
Good luck, let us know which you chose and why.