Airbag light

[phil.s]

I'm picking a car up tomorrow (1.0S 52 reg 3 door) and the seller called to say the airbag light has just come on. His wife took it straight to Nissan who reset it but the light's back on again. Nissan told her it's probably corroded terminal or harness problem. Now, what's the worst case scenario to get this fixed and is it a diy fix? Is the possible offending wiring under the seats and how do I get to it? Your thoughts much appreciated.