A woman on a matchmaking site that refuses to exchange numbers and selfies is suspicious, unless she offers a reasonable alternative.
Should she offer a viable alternative such as providing a social media handle as a means to communicate, or offering to do a video chat, this is a different story.
In such a case, as long as she follows through, this is a legitimate method to verify that she isn’t a catfish.
Not all women are comfortable with the idea of exchanging numbers and selfies with a match.