1. Has the tape cassette been tested?
Asking if a tape cassette was tested is a fundamental question to ask.
Unless you know it has been tested, you may be taking a considerable risk. Though it is very unlikely tapes may be blank after exposure to things that may strip the information off of it. They also might not be able to rewind or play forward. There is another possibility that the sound is distorted or muted.
2. Is the tape stretched?
If a tape is stretched this means that the tape is not going to sound the way it initially did. Sometimes this happens when the cassette is latched onto something and pulled. 
Other times it can be caused by being stuck in a tape deck then aggressively pulled out. With time the tape may become stretched out on its own from an extensive amount of usage.
3. Is the sponge in the cassette?
When you look at a cassette tape on the part where the tape is exposed, you may see a small sponge under the tape.
If you know this sponge, it is a great thing. Any tape cassette that does not have that sponge is virtually unusable. Even if the tape is tested and is claimed to work unless you see the sponge, it would be recommended to ask on the sponge condition
If you’d like to purchase tape cassettes from tapecassettes.com, please see our live eBay listings below. Our products have had the three questions already answered!