You’re spot on when you say pinging won’t be good for the engine long term, but even in the short term, this needs to be fixed to prevent serious engine damage. The best advice is to find a mechanic or workshop that is experienced in this make and model and tap into that experience.

Fundamentally, the main causes of engine pinging (or detonation or pre-ignition, call it what you will) are a lean air-fuel mixture, incorrect ignition timing, fuel with an insufficient octane rating, carbon build-up inside the engine or an engine that is running too hot. None of these things should be hard to spot for the right mechanic.

The government has, indeed, made changes to fuel quality standards, but none of these should have affected the octane rating (or RON) of the fuel. In fact, there are mandated Standards for fuel octane, although that doesn’t rule out the odd bad batch. Do you fill up at the same service station every time? It might be time to try a new one.

I'd take it to an independent Suzuki specialist mechanic, or a suspension specialist, and have them wheel align it for you. They won't necessarily adjust it to the factory specs; they will probably set it a spec that will stop the wandering.

I would not buy a Golf in the second-hand $10,000 range. The Mazda3 is the best car but he'll probably get better value in a Swift, as it's a size smaller. Buying private will mean better value, but ensure he gets an independent mechanical check.