A transaction scene is a scene in which nothing happens but a simple transaction. For beginners, transaction scenes are a dangerous pitfall. When the scene Setup is e.g. a shoe-shop, it is tempting to play a scene about buying shoes, but such a scene is not likely to be very interesting.
Transaction scenes need not be boring, but then we want to see something else happening but the actual transaction. An interesting Subtext may help.
The temptation to take the precious things we have apart to see how they work, must be resisted for they never fit together again --- Billy Bragg