I have the AutoXray and while their instructions and descriptions are somewhat weak, they are at least upfront about the distinction between enhanced PID's and generic PID's. With AutoXray you can pay a fee to "unlock" the enhanced coverage for the manf that they have licensing agreements with, namely Toyota, Ford, Chrysler and GM. I paid around $70 for enhanced Ford and GM and I can see a lot of PID's that you cannot see in generic mode. Things like AC clutch engaged, canister purge, transmission data and so on.
The abiity of a scanner to display "enhanced" data is not something that comes for free. The scanner manf. has to pay to license this data. Some scanner companies have licensing arrangements set up with the car companies. They may or may not have an agreement with your car manf. You need to investigate all this. This is why I am highly sceptical of any scanner claims to provide across the board manf specific enhanced PID's without upcharges.
From what I've seen you are SOL if you have a Mercedes with these type scanners. You have to use OBDII generic mode which gives you almost nothing on the early 2000 MB.