Although I'd never normally touch a Cat D I might be convinced if the repair evidence stacked up, and the price was right; even where you have someone like Loz who knows what they're doing questions should be asked, and the problem is that you cannot always get the answers from sellers, sometimes simply because they didn't ask when they bought their cars. At £13k for a 2006 QP it is tempting to ask.
In a similar vein I recently enquired about a low mileage 3200 with 'full history' (not accident damaged). Low mileage yes, full history? Nope, it's had long periods of lay-up, and the price does not reflect a very tenuous history. I'm not surprised that the vendor can't shift it.
PH