1: Avoid overpaying for low-grade coins.

2: Don't neglect research before buying.

3: Be wary of altered or counterfeit coins.

4: Avoid storing coins improperly.

5: Don't rush into selling without guidance.

6: Mistakes cost money in the long run.

7: Educate yourself before investing.

8: Join a community for advice.

9: Learn from others' mistakes.