I know nothing about them, but condition, authenticity, rarity, and collectibility all matter. That might sound redundant, but here's the thing:
Sporterized, a gun may be in great condition but inauthentic and worth less.
Authentically, a gun may still be so common that it is priced lower.
Even if rare, a gun may still deserve a lower price due to lack of desire for it.
If there's something desireable about these guns, it could still demand a good price if enough people are willing to buy them.
I've never heard of a Syrian Mauser, closest geographically would be Persian, Turkish, or Israeli. What's the caliber, barrel length, and such? Pictures would help greatly.