Essentially, there are two FMP type guns.
The first are actual FMP builds that were imported as whole guns. Normally, they are import marked "Pars", though there may possibly have been a few one-offs that would be marked with some other importer. Either way, "Pars" means it's a factory built gun.
The AWB killed the importation.
More recently, FMP kits and FMP flats were brought in by Century, who assembled them here in the USA. They are still marked "manufactured by FMP", because they built the parts, but they will also be marked "Century".
The "Century" marked guns weren't assembled by a licensed HK factory, using HK trained personnel, nor HK QC standards. As such, they are worth less than the actual FMP built guns.
The Century guns aren't bad guns though. I have one and it's fine. It's not as good as a FMP build, but it's far from the other junk HK clones Century put out. Maybe they sub-contracted the builds or something, but it doesn't seem like the "trained monkeys" put them together. It really doesn't matter, it is what it is and it's not an HK licensed build. As such, they don't command the same price.
Just see what the markings say. "Pars" is worth much more. maybe not as much as a German gun, but not far behind either. "Century" is worth less. Probably under what a PTR would bring.