A lot of the aftermarket bezels and bracelets are just that - aftermarket, or even worse outright fakes when they are stamped G-Shock etc. Genuine parts from official Casio outlets are far more expensive as you know, but they are genuine and fit.
I bought a DLC Bezel, bracelet and male and female screw sets from authorised dealers and they fitted like a dream, but were about three times the price of the shite listed on e-bay.
I have my positive display, full metal, DLC Watch listed for sale on e-bay for less than a third of the price people are asking for a Porter, but stand little chance because people are influenced by the prices of the stuff that doesn't fit.