Yeah, there's lots of problems with this style of piracy. Your ship has to be hanging out in space between the planet and the 100D limit without anyone bothering it. Your target ship has to arrive in the same hemisphere as you or the planet will block the flash. There is then about a million km between "ooh, a jump flash" and "can vaguely discern what that ship is". You have to remain unbothered while accelerating on a course any computer can determine is an intercept, which means you have to mysteriously remain unnoticed while running active sensors and thrust. Then even if it's not a Q-ship, you have the usual issues of matching vectors, disabling the ship, boarding and transferring cargo, etc when the target has had plenty of time to build up velocity.
If this is a complete backwater where the local planet can't provide any anti piracy defenses, the trade is going to be armed free traders or the like. They'll fight back. And they aren't going to stroll down the yellow brick road straight at the starport when they can take a funky route to juke these blind intercepts. M-Drives mean fuel conservation isn't an issue and it is rare that the difference between 5 hours and 6 hours would outweigh safety issues.
And if you are wrong and it is Q-ship or whatever...that's the end of your career because you are deep in a jump shadow when all this goes down.