Many clasp marriages are not malicious attempts to deceive but done out of necessity.
Quite often an original clasp or a reproduction made from the proper material is just not available.
After a short time, you will get a feel for what clasp styles were most popular in that era.
Knowledge of clasp types and the time periods in which they have been the most popular can help you verify the approximate age of a vintage necklace you might come across later on.
As mentioned above, these elements include style, material and maker’s marks, if any.