I usually investigate any signal I am not sure about, but I never dig the target up unless I can improve the target response.
The easiest way of improving the response from an iffy target, is to move a layer of sand away from the target area with your foot or sand scoop.
Moving a few inches of top sand away from the area, will either improve the signal or break it up even more as your search coil is put closer to the target.
Time spent beach or water hunting will help you to tell the difference between good and bad targets.
Knowing what your metal detector is telling you is under the search coil, saves valuable metal detecting time.
Discriminating beach hunters have a huge advantage over " Dig it all " beach hunters who dig every piece of junk while you bypass obvious junk targets.
Knowing how to deal with iffy half way attractive targets will cut down on the chances of you missing targets being incorrectly identified.
Unfortunately, a metal detectors discrimination may incorrectly reject a good target on the edge of detection range.
Getting your search coil closer to that iffy but possibly good target will eliminate that possibility.
It does not take very long to move a few inches of sand away from the area, to put your mind at rest.
I have an ear for most targets at the beach, but every so often I have to just make sure certain iffy targets are what I assume they are.
The beaches you search have a lot to do with how much time you put into investigating iffy targets, you would drive yourself nuts on a tourist beach stopping to dig every iffy signal.
Alternatively on a beach with a little history and very few tourists, signals may be few and far between, and you probably would be using no or very little discrimination.
Nine times out of ten, an iffy signal on a discriminating metal detector is going to be an unwanted junk target.
I never worry about missing the odd good target, or worry about good targets out of detection range.
If I did, I would probably have a finds pouch full of junk instead of the gold and silver jewelry I return home with.
An iffy signal is often a testament to your beach hunting skills, as you know it warrants a closer look.