Inaccessible crawl space
If you can't crawl in it, it isn't a crawl space - PERIOD.  

This isn't an alarming issue.  But you should try to look at it in whatever way you can.  Floors that low to the ground can have dry rot, retain water and can create thermal issues in some climates.  It really depends if it was done right and insulated.

Now if I were buying a home I would almost treat this like a slab.  Know that you may need to tear up the floor to move electrical and plumbing in the future.  Inherently this is a bad thing and should make you think about the value of the home but it certainly isn't a deal-breaker when buying a house.  (Mike Holmes would tell you to dig it down and pour concrete - but it just needs to be insulated really)