This extension looks promising but is like a premature baby. The free version has too many bugs, language errors and incomplete features to give confidence to a paid version. I look forward to upgrades and will come back at that time, but for now, I must remove from my site. Some issues:
1. No user's guide. Some features are not intuitive.
2. No payment method. No point booking on-line if can't pay.
3. Display problems: the object text shows up on deep blue background (my Joomla template is light beige). The print size for "Powered by ARTIO..." is larger than the Object text.
4. Currency symbol can't be placed in front ($). Displays currency values only in European format.
5. English version has too many grammar and spelling mistakes to be usable if not easily alterable.
e.g. Customer registration fields are illogical (Title behind & Title after?)
e.g. "You are no register as customer" (try: "You are not registered as a customer").
Why doesn't the extension use the Joomla! registered user database?
6. Image upload features (e.g. from Editor) don't work. Administrator needs to creat file folders manually to get Gallery button to upload.
7. For programmers, the customization of code to be usable might be OK, but newcomers to Joomla! will waste their time.

I don't think that the demo site was built with the free version. It looks great. It would be better not to release a free buggy version if your paid version in fact addresses these issues. Why kill your market before the extension has had a chance? I'm hopeful you'll upgrade the free version to be useable so I can justify going pro. The 2 object limit should be enough assurance you'll get paid via an upgrade.
Good luck - its a promising start but not ready for prime time.