How not to sell a car

So I’m looking to buy a cheap to take to the beach and fill it with sand and dripping wetsuits. If it gets ab it scuffed, I don’t care. And after a few weeks of scouring the local rag, I think I’ve found the perfect beast – a Ford Sierra 1.8. Yep, it’s old (over 15 years) and a bit tatty, but in my totally uneducated opinion would do the job perfectly. It even comes with a roofrack – perfect for the surfboards and it’s already cheap – the guy has it advertised at £375. Perfect. So having taken it for a quick spin, kicked the tyres a couple of time and sucked a LOT of air in through my teeth, I start to haggle.

“Well mate, I’m interested, but, well you know, it is an old car, the front tyres haven’t got much life left in them so I wouldn’t want to pay more than £300 for it. ”
“Yeah, that’s fair enough, no worries. I’m happy with it.”
“Cool.”
–more idle chitchat–
Him: “I tell you what, if you’re interested, you can have it for £250.”

Should I be concerned? We agreed on £300 for it on the basis of a few faults I’d already identified, yet he then, without asking, volunatarily did himself out of £50! Is he just an idiot?