I recently bought 3 Hoya PRO1 D protector filters from Hong Kong on eBay from hkdirect; they're definately the real thing, much cheaper than any UK supplier and only took a week to arrive!
i bought 2 from DCdirect, the realdeal as well. there is a difference between the HMC Pro1 and Pro1 D and the Super HMC Pro1.
The first one is standard thick glass no coatings...really rubbish, I have seen these get sold on reputable UK retailers for £100+
Then there is the Pro1 D these are thinish glass with coatings they are midrange...I have seen variable prices for these going from £80 to £150 on UK
the last one uber glass, really thin lots of coatings very expensive even the HK ones are equally expensive. (that's how i guage if the retailer on ebay is real deal, and of course the feedbacks) these retails around £150
all in all, you cannot trust the pricing of UK retailers, cos they can put whatever price they like. since that is the case then why is it so different from not trusting the ebay sellers for their product being genuine or not
additionally if the thing is a rubbish piece of glass waste of time, you can tell when u rotate the thing, and also you can tell if it has any effect on darkening the sky etc. the Hoya ones i have are very smooth and very robust. and the CPL works, effects are very evident and there is no vignetting effects.
I would recommend DCdirect, as i have also bought from HKdirect which took well over 1 week to arrive, but HK direct had proper packaging where DC came in an envelope.