My strategy normally is:
a. Everything in black and white (print) from the start
b. Best if subtle "trip wires" are included in communications
c. decide early how many trips need to be triggered to just run away
d. As deal progresses, move to voice contact
e. If deal progresses further, go face to face

If seller is a fast talker, smooth, or over the top "nice", etc, I usually pass, most con men are on their best behavior when dealing.
When seller beats around the bush, don't forget the "bush" is what they don't want to address or you to discover
Listen to your gut.
And worst aspect, good deals don't last long.

Reality check, that half the population is smarter then 50% of the people and it's a constantly contested fact.