If you think it dangerous, there must be a problem. Have you had your tracking / alignment checked? That can seriously affect the 'weight'.
I'd say get a pukka 4 wheel check done, then get back to your seller with proof of alignment if its still a problem. (alignment is afterall just good periodic maintenance anyway)
Best place for you would be
http://www.sapphiregarage.co.uk
Highly rated by many (including Darren Wood BMW), the latest 3D kit, while you wait service.