From what you've described, I'd guess that they are wet-laying their parts and most likely using a polyester gel coat and polyester resins to reinforce things with

This is quite a cheap and easy process to undertake, although I'd guess it would not always lead to the best cosmetic results. Although the gel coat and resin would have good levels of UV stability, it's likely that such parts would show signs of yellowing or milkiness in a relatively short space of time if exposed to the sun for much of their life

An automotive grade clear coat would certainly add a better long-term level of shine, but wet-laying anything but fairly straightforward shapes would be a challenge in terms of getting good weave alignment and would take some skill to achieve