Hi Catherine,

That generation of Insignia can develop an anti-lock brake system fault that results in juddering from the rear of the car when driving along normally. Various warning lights and minor system issues include incorrect tyre pressure monitoring read-outs, airbag warning light, failure of the boot release switch

If there's a vibration through the steering wheel at motorway speeds then the front suspension lower arm rear bushes could need replacing.

If it's difficult to engage gears on the manual car, then it may be necessary to remove the gearbox to fix, which is an expensive job.

You've not told us which engine you're interested in so we'll assume the 2.0-litre CDTi diesel. That has a known issues where the flaps in the intake manifold break off and cause all manner of poor running, also potentially damaging the internals of the engine. That's the major thing to have looked at before committing to buying this car.