internet scams how to avoid??

I've been buy busted up Motocross bikes since we arrive in country almost 2 years ago to make some $$ ( To buy the duster since done that) but usually find if it comes across a little suspect when they text you asking for your bottom $$$ just add a few thousand or more pending on the price you are asking as their english is so bad and they send out so many texts trying catch someone out they normally agree to the price. the other thing I do is call them back if they only text fake ones normally go straight to a message that tells you it came from a PC app.