DG: Out of curiosity, I researched the Fisher 1280X aquanaut and most reviews which I read indicated that it was marginal to not suitable for use in salt water as it constantly false alarmed and was noisy.
The reviews on wet sand at salt water beaches were mixed most recommended staying away.
The reviews were very favorable for use in fresh water wet sand and fresh water shallow water hunting.
The reviews were favorable for dry sand hunting on salt and fresh water beaches.
As you stated your detector is ok on dry sand - there is most likely nothing wrong with it and should be sold to someone who hunts fresh water beaches.
As a caveat, I would like to remark that research on the internet is tricky.
You may of been looking into the wrong places or overlooked the shortcomings as your research was biased. The best place to start is to read the detector's User's Manual to determine if it is suitable for your use as it is more objective than most reviews.
If you don't want to dig every signal, you will need a multifrequency detector for discrimination.
If you dig every signal at the beach, you can detect deeper and get by cheaper with a pulse Induction (PI) detector.
Recommended multifrequency detectors, in production, for diving, shallow water, and wet/sand on salt water beaches are Minelab Excalibur II (nulls on iron, discriminates) and Fischer CZ 21 (discriminates).
Recommended Pulse induction (dig almost all signals) , in production, for diving, shallow water, and wet/sand on salt water beaches are Garrett Sea Hunter Mark II, Tesoro Sand Shark, Whites Surf PI Dual Field , Garrett Infinium LS.
The above detectors are listed in order of my personal preference based on my requirements. You will have to do more detailed research to determine which one(s) best meet your needs.