If there are markings made on any of the cam gears or crank gear (like whiteout markings) it kind of tells you that the belt has been replaced. This is how I knew when I was doing my timing belt that it had been done before. Now, that doesn't necessarily mean that they did the full 120k and replaced all the seals and tensioner pulleys. Just look for little things like that.
"Stance: cuz goin fast cost money yo (n/m) - ZiNnYc 08/09/12 18:23:42"