I have no experience with any of the shipping cart/sales plug-ins. I am helping out my mother-in-law on a site which will sell a very limited number of digital products. I am looking for a quality plug-in, simple to use and maintain, reasonably secure (in the sense that it is not easily circumvented to gain access to the content, although I realize there are other factors which will play a role), and is not significantly expensive. She will be selling a few, relatively inexpensive digital products (and frankly, at this point, I do not expect a high volume of sales) and the cost of a full-blown cart/sales system would be unreasonable.
I have seen a couple of plug-ins which seem to offer some promise but, as I say, I know nothing about them, and there may be others of which I am not aware that are worth considering. I guess I am really looking for a couple of things: If you have used such a plug-in I would like to know which one(s) you would recommend and what you like about them (and also what you don't like about them, if applicable) -- and which one(s) you would recommend avoiding and why (not appropriate for the described use, usability issues, security issues, et cetera).
Thank you in advance.
P.S.: Please do not let the fact that I mentioned that this is for a project by my mother-in-law lead you to suppose that I may be inclined to let this project be less than as good as possible or that I might be inclined to see the project fail. My mother-in-law rarely even strays close to monster-in-law territory. She is my wife's mother after all, and my wife is pretty terrific so how bad can her mother really be, eh? :)