Old or new body stlye? I would stay away from the older body style XC70's
for a number of reasons. I would also ask to look at the service history
and the maintenance book to make sure the previous owner took care of the
car or if the car has a long history of warranty repairs. If the car has
close to or over 60k make sure the 60k service is done(inlcuding the pcv
system cleaning). This will save you a lot of headaches in the future. As
far as the tires are concerned they are pretty decent as long as you keep
the proper air pressure and alignment specs in check. If the car your
considering is the older body stlye expect a lot of edge cupping and wear.
Regardless of which stlye it is when the car needs one or more tires you
have to replace them all due to the angle gear(AWD system) used. This can
get expensive.

The XC70 was the first year of the redesign which was a big improvement
over the previous V70 XC.  I have had 3 trouble free years with this
car.  Mine has 55,000 miles. Gas mileage around town has been 22-23 mpg.  
On the highway it is 24-26.  I love the Pirelli Scorpion S/T 215/65R16
that came with the car.  When I needed replacements, it got another set
of Scorpions.