I've got a friend at work who buys and flips a lot of salvage-title cars.
He drives one himself as well --- Honda Odyssey minivan that he packs his wife and three kids into.
If the repair is solid, and the car hadn't been damaged to the point that you (or a credible mechanic) thinks that rebuilding it was a bad idea...(as in, major front subframe/frame/forward-collision crumple zone damage that required cutting out structure and re-welding it in, thereby possibly causing the vehicle to be possibly unsafe in a subsequent front-end collision....) --- then why not?
Anyone buying a salvage-title vehicle agrees to the "tarnished reputation" of the vehicle in exchange for an often killer price. And anyone who buys it afterward from you does the same. So you're "in" to the vehicle for a lot less coin, and can often "drive vehicles above your means".....
Just make damn sure that the repair is Mercedes-approved. Those front crumple zones are engineered darn precisely nowadays, and the timing of airbag deployment is split-second controlled based on how the energy of the crash impact is mitigated/dispersed through those front chassis structure elements.
In **another** subsequent crash, a repaired and re-welded front structure, if done improperly, can crumple in an unexpected fashion, directing energy into the occupants or simply cracking/breaking away at poorly-done repair welds. It can also have the effect of tricking the airbags to deploy (or not deploy) at the wrong time, sometimes causing more harm than good.
Do you know if the airbags went off? Was it all Mercedes parts 100% that the vehicle was repaired with, at a Mercedes-approved facility?
Figure out (and decide carefully) if the van is convincingly, truly safely repaired to "as safe as when new" standards by reasonable/qualified assessment.
THEN allow yourself the judgement of how great a deal you seem to be getting. A deal's not a deal if you are likely giving up a measure of safety for loved ones who ride along with you.