Just give them a ring on the mileage. If it is high then you know. The price doesn't seem too good to be true at a glance but it does seem very good.
Worth noting that bigger engine rear wheel drive cars don't sell so well on the close run up to winter and possible snow so that could be having an impact but it will almost certainly come down to the mileage.
The traders website looks legit but they have only published the mileage on a few of their cars. There will be a reason for that.