I'm not sure if a cimex would be effective, I've never used one, But I wouldn't use a bonnet on it so I don't know if that gives any clues.
If it looks like it's got quite dirty, i.e. dry soil deeply embedded, it'll definitely need extracting.... but DO NOT get it wet until you've backdusted the living bejeezus out of it. Otherwise you'll end up with a disaster on your hands!
I had to walk away from a potential £100 earning on one of these because I simply didn't back-dust it effectively enough, and started extracting it only for the pile to turn a horrid grey colour which I couldn't rinse out. I had pre-qualified possible failure with the customer, who was about to skip the thing, so nothing was lost, I just wanted to have a go. This was quite a few years ago, if only I'd have had my Royal both I and the customer would have been a bit better off!
The problem is the sheer length and density of the pile, there's probably a family of ferrets living down there trapped under all that pile. If you haven't got a rug badger or decent upright vac to knock out the dry soil, it'll need manually beating like hell.
Although you might be tempted to use your hand tool or stair tool, I'd stick with the wand. A glide most definitely helps on these.
Obviously this is all presuming it's in a crappy old state, as most of these end up. Cost might be a preventive factor, if they paid £100 for it you should probably be charging the best part of that to clean it properly, it'll take you a couple of hours.
However being optimistic, if it's in good nick, just a simple shake upside down (spend a good few minutes doing this) and then vac & extract, should bring it up nicely.