Yes, many people will take the largest script the doctor will prescribe. Insurance generally helps cover the cost of the prescription, so reselling them can be really lucrative. Even in your scenario, 25 pills seems like a lot. Many people will be totally pain free in 2-3 days. No one needs 8 pills a day for wisdom teeth. Let's say they take 4 a day for 3 days, that's still 13 pills leftover.

Go to any manual labor job (construction for example) in the Midwest. You will find people wanting to buy leftover prescriptions and people selling them. It's a pretty large black market. The vast, vast majority of people I know doing construction, laying asphalt, etc are all daily drinkers, potheads, or addicted to opiates. It's honestly super depressing.

Wow. I had my ACL done and got 3 days worth of Oxycontin (6 tablets, 1 every 12 hours). I didn't want to finish taking them because they made me hallucinate. Looking back, I probably could have gotten by after the first day with only ibuprofen. The doctor was very concerned about staying ahead of any pain though.