Air Bag Light flashing (but it is more than the switch under the seat) PEU 306

Today i took my car to a PEU dealer in Malta to fix the flashing light
and i was shocked by the news that i had to pay Eur 528 to repair it.
Basically they are saying that they diagnosed the problem to be that
the car had an accident (i bought it second hand so i do not know the
real history but it does not look so) and the seatbelts were trigged
and thus both seatbelts + the ECU (must be the electronic part) must
be changed.

I'm confused about what to do cause on the one hand i can't trust the
previous owner saying that the car was never involved in an accident
whilst on the other hand i'm skeptical about the diagnosis results.

Is there a way i can manually / visually check some things ?
Do you still recommend that i should eliminate the connector under the
seat ?

Your advice is much appreciated.....

 

usually if the pretensioners have been fired you can see the plastic
around the stems is "concertina'ed"

 

Can anyone tell me in more detail how to check the pretentioners ?