Costco (COST -1.34%) is a retailer that every investor should take the time to examine. There are two very important reasons for this, and both are logical reasons to buy the stock. However, there is also one very big reason why investors might want to wait.Here are two reasons why you might want to buy Costco, and why you also might want to wait until some future tomorrow.1. Costco has a very strong business modelThe most important thing to remember about Costco is that it is not your typical retailer. It ...