[A4] Want to purchse A4 Questions

[sub]

I currently have the 1993 90CSQ and I love it !
Now I am interested in purchasing for my whife an 1998 or 1999 A4 2.8 
Quattro
(I figure that the 2.8 is less headache )
My questions are in regard to authenticity of the vehicle:

How hard or how easy is it to fudge the milage on the car ? how worried 
should I be about this ?

is there any specific problems with these models ?

is there any thing that I should specifically look for ?

any ideas and help is greatly appreciated

Thanks