The issue isn’t shaveh p’rutah, it’s s’michas daas. IOW, if the marked karatage is wrong, there could be an issue. She may assume, for instance, that the ring is worth $150, and only be meksbeles kiddushin on that assumption, yet the ring is only worth $18, so the kiddushin would be invalid.
Easily fixed by (a) ascertaining that it’s worth a minimum of a shavah pruta and (b) asking the kallah under the chuppah if she accepts it for marriage whatever its value is (subject to the shavah pruta minimum).
The Wolf