It's Super Customizable, and the Author does provide 5-star support!
I have a special requirement for my sales "items", being the fact that my customers need to buy concert tickets for different "concert dates" at different locations, AND with multiple ticket types at different prices. Nearly all other 'shopping cart' software packages force me to create one-event-per-performance, because they don't support different pricing for each "option" when multiple options are present (With this one, a single Concert "Product" can have a 4*5 array of uniquely different dates, and ticket pricing levels, quickly grabbed by pull-downs).
The admin GUI is complete, fast, and easy to use. His support is top-flight, but the *features* and *ease of use* were the keys to my purchase. My thanks to Mr. Khorev, this is wonderful.