Here's what to do:
Ask the person to upload a photo to their profile holding in front of them a sheet of paper handwritten with the words, "I am not a Romance Scammer!" If they delay, protest or outright refuse, they may be a scammer.
Also, if their already uploaded photo(s) have their heads cropped off at the neck, be suspicious. Personal vanity would usually prevent them uploading photos appearing headless.
And finally, and I cannot emphasize this enough, use Google Image Search to see if their photo(s) have been uploaded elsewhere. If the suspect photos appear to be copied from inconsistent sources, that may be a red flag.
Thank you for your attention, and please be safe!