Yes, this is no problem at all. Basically... here's how you would do it:
1. Purchase your license.
2. Upgrade the installation on your potential client's website using your license.
3. If they like it, then you (or they) buy their own license. Now you replace the license currently being used with the software to the new license.
4. You can log into your customer account (
http://www.snippetmaster.com/customers) and "re-issue" your own license, so it can be used again with a different website.
5. Repeat.
I hope that makes sense? In this way, you can use the same license for each new website by "re-issuing" the license. (Each time you "re-issue" the license, it clears the current website information from the license, so you can use it for a different website.)
If you have any questions about anything, just let me know.