Well the bolt pattern is the same. The back spacing on these is 35 I believe. They're in good shape so the 2800.00 for perfect ones is not what I'll ask. I think $1500 with tires is good. Two are new.
I wouldn't use the term Backspace, although it exists, it's a different measurement from Offset (ET), and is not recorded on the wheels anywhere.
Backspace is a measurement needed to calculate the Offset.
Just about all Mercedes wheels have the Offset(ET) cast into the back of the wheel, and most likely all three measurements are together like this;
7 1/2J x 17H2 ET35 (Fronts in this case)
8 1/2 x 17H2 ET30 (Rears of a staggered set)
To properly identify any wheel, give all three measurements, rim width, diameter & et.
With that information a buyer can figure out if they fit his car.
If all 4 are the same, you are selling 4 front rims from C36/43 staggered sets.
If you were to pull one of the wheels off the car, you would most likely find the size on the back of the wheel as depicted in this picture.