The easiest way to find out if you have them is to take out your acro's that you can and drop them in a bayer dip for 10-15min, then rinse them off in display water in another container, then add them back to the tank after they soak. Then check to see if any AEFW fell off. They will come off with basting but not always. You also can't think that because you have a 6 line or corris...etc that they are eating them. AEFW are extremely camouflage for a reason.
And like mentioned above, your LFS could just be clueless : ) hopefully this is the case. You can't accuse someone of having AEFW and not show them proof. Could have been a way for them to try to get your frags for nothing.