1. A hassle-free installation of the extension
2. An intuitive way for your customers to make a purchase
3. Some support from the developer should there be an issue.
Documents Seller is one of the most powerful, well thought-out extensions I have seen in years, delivering on points 1 & 2 flawlessly.
Tuan, delivers on point 3 with such professionalism that you realize instantly why points 1 & 2 are so effortlessly there.
As it happens, I happened to have a request which had not been catered for. Tuan turned it round within eight hours and made it available for download.
This is high-quality work, backed by rock-solid support. Definitely deserves your support and deserves to do well. One of those times when I can say with total confidence that you will not be disappointed.