Les
I would tell the customer what you think will happen to the rug and let him make the decition, as jim says.
I have cleaned loads of these, yes they can shrink but if it distorts it is probably a "trainee" rug.
I would first check for colour run, if no signs then as long as you keep the solution neutral or better still on the acid side.
Vac it really well, and then some more and what i would do is to lightly mist over with chemspec oneclean traffic clean or prochem bonnet, rub over with a terry towel, then rinse with either acid rinse or chemspec oneclean.
The rug will go really stiff when you do this but as it dries it will go soft again, anchor one edge down and as Shaun said put turbo over/under it this will then "shake" it and probably wont distort.
Regards
Daryl