First, try to buy new tickets, which is relatively safer. For some countries with stamp industry, such as Tanzania, Kenya, Sierra Leone, Guinea Bissau in Africa, Saint Vincent, Grenada and the Grenadines in America, most of the "commercial tickets" issued after the 1970s are "stamps", but they have almost no postal value, so it is best not to buy them.
Second, you should be able to buy tickets with confidence.
Third, it is not recommended to cancel the ticket. If you want to buy, you should also pay attention to the countries mentioned in Article 1. Most of the fake tickets seen in the market are also concentrated on canceling tickets. If the postmark is printed directly instead of stamped on the stamp, it can be considered as a fake ticket.
These are just some experiences of simple purchase. It is very learned to really distinguish authenticity, especially the authenticity of some classical and semi-classical stamps.
For beginners, it is best to buy relevant authoritative catalogues, such as Scott in the United States and Gibbons in the United Kingdom. As long as it is included, 90% can be confirmed to be true, but it cannot be completely considered that these authoritative catalogues are not included, which is a fake ticket. For example, the stamps in our liberated areas are not included.