Higher temperatures accelerates corrosion and I see at least two indications of overheating in that photo. I'd be suspicious of any sparky wanting to sell you a new panel when he can't give you a decent reason what went wrong with the current one.
With just the one photo to go on, I'll wager the connections weren't good enough to prevent overheating. Decades of making lug connections in industrial settings well in excess of 500 amps has taught me that the lugs should be re-tightened after a few weeks. They tend to loosen for reasons I've never clearly understood.
I suspect the panel can be saved. It just needs to be cleaned, the corroded lugs replaced, excessively corroded copper replaced, and every last connection checked.