HA! I just wrote this to a guy yesterday about how he should judge what a woman wants, and what he wants - through actions. Obviously this takes more time than just reading a text, or even having a single conversation. This is not just for romantic relationships.
I go to the gym a lot and thus meet a lot of "gym buddies." People I know by name, say "Hi" to and have short chats. I only have deeper friendships with those people who actually take the time and interest to learn and ask something about me when I do the same.
If someone only wants to talk about themselves and/or doesn't respect my time, then clearly they are not into me. These are not potential romantic partners, but the same principle applies (IMO).