If he sells gaming PCs why has he taken a photo of the insides of a stock Acer Aspire? Avoid. A gaming PC that cheap (especially prebuilt) will be terrible. He may well get 25fps in GTA4, but at rock bottom detail settings, i.e. worse than the consoles.
you should just contact him and ask about the parts he uses in the system. then if you see any questionable parts, like a cheap power supply, then i wouldnt go for it
For that price, a cheap PSU is guaranteed. I've seen 'gaming rigs' built for four figures that still use Coolmax PSUs. If they don't tell you the brand of the PSU, it's for a good reason.
Not only is the PC guaranteed to be terribly slow and of poor quality, the green tubing in the case seems to have no purpose. I think I see a loose end just hanging there. Like my good buddy Sam suggests... avoid it like the plague.