The deployant (folding) buckle
It can be single or double according to its construction. It will show normal signs of wear depending on how the watch is used and how carefully the buckle is opened and closed. A badly-closed buckle increases the risk of knocking and damaging the watch.
The pin buckle
It can show signs of wear in the form of scratching and dents. Check the holes in the strap for wear and check the pin which can get bent out of shape. If the buckle no longer fastens correctly, the watch can slip off the wrist and be damaged or lost.