Some places will just point you in the direction of a web site that you could have found on your own with a little effort. Even then you are not going to get detailed criminal records, like Razorguns said, they are off limits.
All these companies do is simply buy databases from various counties, cities, etc. Then they try to make them all compatible for searching. Even then -- with all these databases -- it probably only acounts for 20% or so of criminal records. And that's a liberal figure. At best -- they're usually latest as of 6 months ago.
There's no still no national database yet of pure criminal records. Only the FBI has a national database that cops pull -- and that's up to the minute -- and off-limits for private individuals/companies.
Warrant information, for security purposes -- is also off-limits.