Honestly the security guards at the grocery stores I've been at have mostly seemed like just people doing the absolute minimal to watch the front of the store and monitor and deescalate for any actual violence or harassment (unfortunately usually from homeless and other very hard done by people with mental illnesses). My experience was that loss prevention who watched the security cameras from their offices and stalked and chased after people were the real villains. I guess these roles may overlap depending on the store though.