Edit: About trust, and planting it: pick up some of the more known or larger institutions from the Moodle Sites list and say "Look, they are using it too. It must be good and trustworthy".
One important factor is to emphasize that there are a lot of companies that provide commercial support for Moodle. (Some of them are listed at http://moodle.com) This way you get both the corrercialism and the "socialism 
". With Moodle you can choose to be somewhat locked in to a product/platform, but not at all to one single company. With WebCT (only for example, again) you get locked in to both, so it would seem like a more unconformtable situation when thinking about "what if they drop the product/support?".
Edit: About trust, and planting it: pick up some of the more known or larger institutions from the Moodle Sites list and say "Look, they are using it too. It must be good and trustworthy".
Edit: About trust, and planting it: pick up some of the more known or larger institutions from the Moodle Sites list and say "Look, they are using it too. It must be good and trustworthy".