Worried that your good deeds on Earth won't guarantee you a place in heaven? Fear no more.

A Seattle-based company is offering to hold a spot for you at the pearly gates, and it will even throw in a money-back guarantee. ReserveASpotInHeaven.com sells "travel kits"— complete with boarding passes, certificates and "Heaven 101" booklets — that offer the "chance to enjoy your sin-filled life" without consequence while lowering the "risk of eternal damnation."

The kits are intended to be gag gifts, but some critics don't think there's anything funny about getting into heaven.

The reservation packages have been a big hit this holiday season and sales have been brisk in the month since the company launched, according to the creators. The number of visitors to the site has gone from 80 the first day to a few thousand daily, they said.

"We don't want people to take it seriously. It's more of just a fun idea we came up with that we thought we'd turn into a novelty gift," said Edgar Kim, 22, a retailer by day who started the business with his childhood friend Nate Davis, a 23-year-old product designer. "We're not trying to offend anyone or anything like that."

But they are offending some people, nonetheless. The company has been blanketed with a steady stream of hate e-mail, calls and message-board postings from those who find the site insulting.

"Your marketing of 'tickets to Heaven' is absolutely one of the most asinine things anyone could ever do; to disrespect something as sacred as Heaven and God's grace," one naysayer wrote to the company's "comments" address.

"You are making a mockery of the salvation only God can guarantee us. ... I am absolutely disgusted with your immoral conduct and hope God will have mercy on your soul."

The site also drew angry responses from listeners when it was featured on Seattle's KISS 106.1 FM. A woman named Amber who called in to the show railed against the concept.

"I think they're basically securing themselves a first-class ticket to hell for doing that and mocking God," she told the DJs. "Obviously, they don't have a genuine relationship with God or know anything about Christianity, because they're completely ruining it."

While some members of the general public have accused the company of sacrilege, a number of religious groups find the product benign and even applaud the developers for furthering discussion about the after-life.

"This isn't something we'd be concerned about," said Catholic League spokeswoman Kiera McCaffery. "We see a lot of silly, dumb stuff like this. We would like to focus instead on the bigger issues."

Focus on the Family, a conservative Christian organization, said it wasn't aware of the site and declined to weigh in on it.

And Fuller Theological Seminary's film and religion think tank Reel Spirituality believes that a business like Reserve A Spot In Heaven can promote healthy dialogue about spirituality and faith.

"Christianity at its worst has often characterized salvation as a transaction that guarantees heaven rather than the initiation of a relationship with a loving God forever," said Robert K. Johnston, a professor and the group's co-director. "The Web site is a humorous spoof on some of Christianity's tool kits for salvation. It's probably all in good fun."

Co-founder Kim says he was raised a Baptist and still believes in God. His online business purposely mentions nothing about Christianity or any other specific religion.

"We don't affiliate our site with any gods or Buddha or anything like that — I made it a point not to do that," Kim said. "I believe in God; I'm not an atheist or a crazy Goth. And there are people who are hard-core religious who are helping us out. Maybe we have a unique way of thinking about it."

About one out of every 10 e-mails that come in complains about the idea, he said; most mention the Bible. To date, no one has written in the name of Islam, Judaism or any other religion aside from Christianity, Kim said.

When it comes to heaven, one price doesn't fit all. Reserve A Spot In Heaven's basic $12.79 "Essential Travel Kit" comes with an "Official Certificate of Reservation" with the recipient's name written in, a "boarding pass to heaven," an ID card and a Heaven 101 instruction booklet to "prevent culture shock," Kim said.

An additional $12.16 buys an "All Access" package, which includes a framed certificate and a "VIP pass."

"That means you can hang out with Tupac (Shakur) and all those people," Kim joked. He said that he and his partner are working on a third, "Frequent Flier" option that includes T-shirts and a heavenly "flier's license."

Reserve A Spot In Heaven has not received any complaints with the Better Business Bureau, according to a Seattle BBB representative. But satisfied customers? That's a different story.

"I thought it was hilarious," said manufacturing technician Michael Rider, 23, of Seattle, who's bought about eight of the express kits for his coworkers, his grandfather and himself. "It's my type of sense of humor. It really kills me."

As for Kim, he's hoping he will get into heaven one day, but he isn't taking anything for granted.

"I don't know — I've never met the guy," he said wryly. "I'm pretty sure if He's got a sense of humor, He'll like me."