There is so much conflicting information about who can recite what mantra that it's no wonder people are confused. All my readings indicate, for example, that the Gayatri Mantra can be recited by anyone, and should be, at least three times each day. It is supposed to be recited at the solar junctions (for lack of a better term): sunrise, noon, and sunset.
I've read that OM should not be recited by just anyone, because it focuses on the unmanifest Brahman, it can upset and uproot one's goals and focus. Other things I've read say that OM, like the Gayatri Mantra can be recited by anyone. Lord Krishna says that focusing on the unmanifest is difficult for the spiritual advancement of the embodied; difficult but not impossible nor forbidden. Can I provide sources? No, because these are things I've picked up in my readings over the years. It has all stuck in my mind because of the conflicting information.
I mentioned before that the Shaiva priest told me to recite Lord Shiva's moola mantra 1008 times, in front of Lord Shiva's sanctum for the benefit of my injured shoulder. Panditji knows I am Vaishnava. Seemingly he sees no conflict. I've read that even a Vaishnava should recite Lord Shiva's mantra for the benefit of controlling the mind and for becoming a better devotee of Lord Vishnu. I wear a rudraksha mala as well as a tulsi kanthi. Lord Shiva tells Maa Parvati that everyone can and should wear rudraksha. I've read some items that say only a strict Vaishnava can wear a tulsi kanthi; others say anyone can and should wear it as a reminder to stay on the path of devotion to Sri Radha-Krishna.
Someone told me that all food must be offered to God; one is not supposed to even taste the food while preparing it. While it's true that God does not need to eat, because we are treating God as an honored guest, would anyone feed distasteful food to a human guest, much less to God? Someone else said their guru said that if they are offering food to him, they better well taste it to make sure it is palatable.
I was told by a woman in temple that one is to never turn one's back to Garuda. She said he will never forgive it; even Lord Vishnu will forgive turning your back to Him, but Garuda will not. Yet the way the sanctums are placed, there are times, especially when receiving prasad at the sanctum of Sri Balaji, that you cannot help but have your back to Garuda's sanctum. Poor temple design? Maybe, but is it for us to judge?
The internet is a great resource, but everyone is an authority, especially when it comes to something as deeply personal as religious and spiritual beliefs. There's a television commercial wherein a woman says she got some information from the internet. She says you can't put anything on the internet that's not true. Sadly, many people believe that.
So you see, this is a large burr under my saddle. Especially all the "you can't so this", "you can't do that", "you have to do this", "you have to do that". Whom to believe? Your heart, and what you think God is telling you. If you derive peace and grace from something, and you have a good feeling God is pleased, do it without flouting some basic rules. If you have a bad feeling about something, don't do it. Take all this with a grain of salt, because it is just my view and understanding, not to mention a rant as to why people, especially newcomers who want to take everything in and "do the right thing", are confused.