First make sure that the wattage figures are RMS values, or in real terms you may find yourself with only 150W Speakers

. Skytec like a lot of manufacturers tend to use and publish their budget range using "Peak" or PMPO values.
I can offer a like for like equivalent from Soundlab brand new for slightly less than £350, so 2nd hand the Skytec is not that much of a bargain!. I would get him to lower it to around £250 - £300