During the pandemic, the main function of the cheap masks was probably to protect other people a bit if you were infected, or even make them feel less scared (like airport security). They probably helped a bit over no mask.
A badly fitting disposable mask probably isn’t going to do too much against an airborne pathogen if you are surrounded by it in sufficient quantity, but maybe it stopped the pathogen being in the air as much / stopped people touching their faces etc, or the masks made people feel safe and like they were doing something.
Proper respirators don’t tend to filter exhaled air (so may let more nasties out easier) and may make people feel scared as they are anti security-theatre. You are actually well protected if they fit you properly but they would appear make other people unhappy / scared if they don’t have one.
If you want more chance of getting a genuine mask compared to amazon, then find a local reputable business or chain in a town near you where tradespeople / contractors go. Preferably an authorised distributor.
Chances are that if you buy a mask from there with the ratings and markings that you want, then it will be legit if it is from a known brand, and have gone through third party testing by a competent authority. Contractors buy the masks all the time for themselves or their crews, so that they don’t get work related respiratory illnesses, have a long career, satisfy OSHA etc. and not get sued.