Having a good seller policy may not sound all that important, but it is. Informing the buyer on how you operate can be the difference between them buying your product or moving on.
Here are a few tips.
First, be sure to mention what your turnaround times are. For example, if you usually ship products within 1 business day, you should highlight that.
Be sure to include a range of your shipping fees. If you offer free shipping, be sure to state that as you know buyer typically factor that into the purchase price of their cards.
Mention where you currently ship to. Is it only the US or will you ship internationally?
Be very clear about your return or exchange policy.
Lastly, consider talking about your images. If you use a lot of stock images, be sure to guide buyers on typical sections that you may use, for example, many sellers use stock photos for "commons". It is also a good idea to reference the condition in the title.