We're certainly familiar with this sales pitch. Is there any truth to it? (hint: no)
One of the things we looked at when we were starting BetterWorld was an analysis of competitor sites that would make claims like this. The key question was "What percentage of an item's Fair Market Value did the item end up going for?" We use this statistic to measure the actual effectiveness of an auction platform. I think [a certain competitor that loves to make this claim]'s average was around ~35%. Ours range from 80% - 130%.
Here's the other part about the "Community of Bidders" line -- those are your donors that they're including in that (whether you allowed your donors' information to be shared or not!) The stat comes from adding up every person that has ever participated in a campaign on their site and calling it a "community". As you can imagine, the real engagement with this "community" is about 0 ... and 99% of the people that are browsing aggregated sites like this are bargain hunting.
It's just our opinion (and our research), but it's snake-oil.
Here's the truth:
Aside from an intuitive, easy-to-use, and attractive platform that saves you a ton of time (<- our pitch for BetterWorld), there are really only a few fundamentals that govern how successful your auction will be. First, it's making the items look great (taking the time to do great copy and have nice images that sell the experience. (Relatedly, there are a bunch of ways to up-sell items ("Hot Air Balloon Trip" can become "Sunset Hot Air Balloon Adventure with Champagne" and raise 3x the amount)). Second, it's opening the auction for at least 7-14 days and starting the bidding low, so that lots of people can come and participate. Finally, and most importantly, it's about leveraging your network. Asking supporters to share the auction on social media, asking item donors to share the link to their item on their own channels, asking your board to tweet or post as well. Good items + good design + good writing + lots of publicity.