"they may have had more highway use than stop and go city (which means engine doesn't have as much use/chance to warm up on cold starts)"

That's a quote from another thread I was reading don't know if it's true but could be taken into consideration.

that is why a had considered this because a trip that is somewhere around 500km and travelling that every week consider that the x5 has had an easy life with no use of its v8 power.

I would think the same but it depends on how the previous owner(s) treated the X.

he has said that he has maintained it from the dealer

Did you get the service records from the dealer? That would be a good idea because it will tell you everything which has been done there.

its a private sale and i will be meting the seller this weekend to look at it

you can still get the service records read from the dealer even if it is private sale. Why not just ask the owner to get a print out of the things which have been done when the owner goes to the dealer to pick up the x5 after the inspection has been done?

Agree with BMWLOVER, owner might not be trying to hide anything and be 100% honest, but there is no way he/she is gonna remember every last thing that was done to the car during it's maintenance life. And I've yet to ever meet a seller who had all the records in perfect order. Either get the full printout from the dealer yourself or have them do it.

As far as what major could go wrong, you should realize that the BMW's of today are not the same ones of 20 years ago. Everything is electronic. Fixes sometimes involve reprogramming and not mechanical repairs. You could have problems with any major system and diagnosing the problem to fix it will cost a pretty penny. Yes the car could be trouble free for the next 500,000 miles, but unless you have money to burn I wouldn't bet on it.