Not reading the full thread but probably the phone won't ring/ messages won't deliver/ you won't get replies pretty consistently (around work hours/ any commitments). Could be they're a slow replier by nature, so not that in itself, more that you'll get flurries of messages then nothing.
Similarly if they try and use text not WhatsApp. Could be genuine but the vast majority of people have smartphones and WhatsApp these days.
Alternatively, Kik is big with cheaters as I innocently found out years ago.