Timing

Timing is critical when investing in sports cards. It is important to know when to buy and when to sell, it is one of the key elements to becoming a successful investor. I will give a short list of good times to buy and sell.

Buying:
-Offseason (there is usually less demand for players now since they are not playing)
-Playoffs for a non-playoff team (buyers are focused on the playoff teams and often forget about the others)
-Injury time (prices usually dip during this time and rise when the player returns. The more serious the injury, the larger the drop)
-Any abnormal drop in prices compared to previous sales (sometimes prices may drop unexpectedly, making it a good time to buy)

Selling:
-Playoffs (plenty of attention/recognition given to players along with a huge increase in demand)
-Strong performances (nothing generates a stronger demand than several good games)

Once timing is perfected, making money is easy. One thing to remember is to never be greedy. If you are happy with the profit (which you should be), then it is never a bad time to sell since prices will come down again. The last thing you want to do is hold too long and have the prices come back down, which happens as soon as the supply overcomes the demand. So take the money whenever there is a good return since you will almost always be able to reinvest when the player cools down again.