Sounds good but exactly how old is it? What reg? It has a big bearing on the price!
You should ask the owner if he has proof of the water pump changed for the metal impellor type too.... If it hasn't, then walk away.
Any decent Alfa independant or main dealer would change it as a matter of course so no water pump change, then the recent cambelt change is pointless and not done properly IMO.
Check the clutch operation and also check if it has been changed, They are a pig to do and very expensive... 75,000 miles is about the upper limit for the clutch so be mindful of it.
Ask to see the service history plus parts reciepts to double check that all six spark plugs and the oil filter have been changed, you'd be surprised how many owners and garages skimp on these parts just because the rear cylinder bank is difficult to get to along with the oil filter!
Check the gearbox oil dipstick, making sure its clean and topped up properly, a sure sign that the car has been looked after!
Check the radiator... A weak spot and only around £100 to replace. Get the car up to temp and see if the fans are operating a lot on tick over.... Every 30 seconds or so and you have an issue with the radiator/ fan resistor/ thermostat so bear that in mind.
If it has a sunroof fitted lift the front carpet and double check the inner driver and passenger front footwells for rust... It may look fine underneath but they can rot from within due to sunroof condensation dripping down and soaking the carpet.
Check that the exhuast is in good condition... Front pipes and flexi joints can be a chew on to replace...
Apart from that, they are truly a great car and you will know what else to look for with already owning a 156.
Depending on the age, a good v/y plate with 100,000 miles can go for as little as £1,200 FSH and cambelts/clutch and all the above done.... So, take that into account. The seller is maybe trying to recover some of the cambelt cost.
If any of the above hasn't been changed in the past two years or so, then you have a good bargaining tool to get the price down a little
Good luck and I'm sure you will love it