Is this true about brushing your dog’s teeth?

Unfortunately my dog is three years old and brushing her teeth didn't become a habit (i plan it to). When she was a puppy it was hard to do it and i ended up putting it aside until it never happened. It is even harder to do now that she’s an adult dog. Anyway I've been watching a lot of brushing your dog’s teeth videos on youtube and one of them said i should check her teeth first and if it you see something is wrong you should get it checked first because if you start brushing right away it might get to the gums and spread and get worse. It makes sense but my boyfriend just told me he doesn't think some brushing would hurt. I also can't bring her to get her teeth fixed right away because i need to save for it first. What do you think? Should i wait to get her teeth checked or am I overthinking it?
Is this true about brushing your dog’s teeth?
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