Courts deal with that problem every day. It is possible to determine whether or not someone is telling the truth, the question is how reliable that determination is.

Actions speak louder than words. If someone says they love you, you know they love when they act that way. Likewise, if someone says that a particular movie is good, you know that they like it if they watch it again, or watch very similar movies.

To me there's no point in trying to determine whether that is true or not. If they know they're lying that's their problem. I can only verify their words supported by facts. If something they say cannot be supported or debunked by facts then I can only hope it is true.

For example, if someone says they love you or that they find a movie really good, how can you ever know they're not lying, since you don't have direct access to their minds? — AnonThinker25

Well maybe not yet.

Team IDs Spoken Words And Phrases In Real Time From Brain’s Speech Signals

What if we could measure intent to deceive along with those spoken words?

I wonder, if feasible and accurate, whether involuntary use of a brain scan will be held as violative of our 5th Amendment rights. Remaining silent will take on new purpose.

For example, if someone says they love you or that they find a movie really good, how can you ever know they're not lying, since you don't have direct access to their minds? — AnonThinker25

You can't. You can try to make sure, however, that it does not matter either. As long as what you really try to get out of the situation, are verifiable results, then why would it even matter?

https://thephilosophyforum.com/discussion/6432/can-you-ever-correctly-determine-if-someone-is-saying-the-truth-when-they-share-their-opinions

No. Nevertheless, if one never meets with a contradiction to the stated opinion, he can assume the opinion is grounded in a subjective truth.

If you can't determine if the other person even exists, it's going to be hard to determine whether they're being honest or not.