Contact the seller to see if they have another key or can explain the situation.

The only lock that you will not be able to fix easily is the wagon tailgate lock. All the other locks are common with sedans and available from the dealer.

I suspect that your ignition tumbler was replaced with either a used tumbler and the keys that go with it, or a generic tumbler and keys that go with it.

In your shoes, I'd order a replacement key from your local MB dealer (bring title and registration, in my area they like registration but others prefer the title it seems). That key will be "VIN-coded" to your car and should match all the locks. If that opens the doors and rear hatch, then you can go back and order a replacement ignition tumbler, and once installed you'll only need one key for doors and ignition.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC