AN ACTIVE ONLINE forum can serve as an extension of good customer service as well as a low-cost way for small companies to drive sales.

That's what ScubaToys.com has found. In June, the online scuba-gear retailer set up an online forum for dive enthusiasts which now has about 3,000 members and receives about 20,000 posts a month.

"If you're buying a $2,000 [piece of] equipment and diving 100-feet down, with your life depending on it, you want to trust the person who is selling it to you," says Larry Dague, owner of ScubaToys.com. The online store and its brick-and-mortar location in Carrollton, Texas, together bring in about $5.5 million in annual sales.

Mr. Dague, a 49-year-old self-taught technophile, started the forum with about $200 in software. In its first month, he spent five hours a day tweaking software, setting up forum categories and responding to customer questions. Now he spends about an hour a day.

WSJ.com asked Mr. Dague about how small companies can build a strong online customer forum. Here are some of his tips:

1. Offer incentives. "Building that relationship with customers is really important, but getting started is the hardest part," Mr. Dague says. "If there's no community, it's a problem. It's the snowball that never starts rolling."

To jump-start his forum, he offered customers a $10 gift certificate for their first 10 posts. He later upped the ante by kicking in a $50 gift certificate for 250 additional posts.

The incentives, which are still in place, can help pay for themselves. The average person cashing in the $10 gift certificate spends about $150 on ScubaToys goods. Customers who earn the $50 certificate buy on average $650 in merchandise.

2. Be a light-handed moderator. Don't be a censor. Mr. Dague takes down only personal attacks on individual members and inappropriate postings, such as spam.

When customers write about a rival business and its goods, he won't remove the post. "I believe it adds honesty to the site, so that people know that my site is not just an ongoing ad for me," he says.

He often comments on such posts, offering to match a deal or a discount on pricing or delivery.

3. Respond to customer complaints immediately. Occasionally a customer will receive an item he didn't order and post about it on the forum. Mr. Dague responds to such posts quickly, saying that he's sorry and already shipped the correct product.

4. Let members represent you. Mr. Dague invites some loyal and frequent forum contributors to be moderators. He'll first read about 100 of their posts in response to customer questions. The test is whether they "mirror the image I want for my community," he says.

Forum members vote on the best post of the month, and the winner receives an item worth up to $500.

Some customers also have asked for and received his blessing to form groups for ScubaToys on social networking sites, such as MySpace. These pages give customers a chance to spread the word about his store and give them a kind of ownership in the business.

5. Embrace popular technology. Mr. Dague recently created scubadivingtube.com to allow forum members to post their own diving videos, rather than to YouTube, and drive traffic back to his online shop. He also will be posting instructional videos related to scuba gear.

But, Mr. Dague cautions, if your customer service isn't up to par, or you don't like to read what your customers say about you, online forums probably aren't a good idea for your company.

Write to Raymund Flandez at raymund.flandez@wsj.com.