No.

Common misconception. All they need suspicion of activity. If there is a pattern emerging, example a guy does a lot of deals on a specific street, or out of a specific car, they can certainly make a move if they go 1 mile over the speed limit.

Then there are dealers who use people's paranoia to their advantage. Especially on deals that involve no scales, pressuring people to buy a bag without throughly inspecting it for quality and amount. Watch out for these guys.

All deals should take place in an enclosed area where there is no element of pressure or paranoia. It makes everyone safe and happy.

Still it's weird to tell a dealer you want a quarter of marijuana. It should come a point where the guy knows what you are talking about without saying a slang word of some sort.