Through Thursday only United is offering up to a 100% bonus on purchased miles. But there’s a catch.

If you get the 100% bonus then miles are 1.88 cents apiece. That’s the regular price US Airways offers miles at, pretty much every month, with their promotions.

And you may not be able to get the 100% bonus. It depends how many other people buy miles. You need a critical mass of others buying to get in on the deal — sort of like Groupon, but:

• Groupon is so four years ago.
  
• Groupon didn’t charge you unless you could get the real deal.

Here’s the bonus table:

• 1-300 people = 35% bonus
  
• 301-600 people = 40% bonus
  
• 601-900 people = 45% bonus
  
• 901-1,200 people = 50% bonus
  
• 1,201-1,500 people = 55% bonus
  
• 1,501-3,000 people = 60% bonus
  
• 3,001-4,500 people = 80% bonus
  
• 4,501+ people = 100% bonus

Will over 4500 people take the plunge? That is a very bad idea.. even if a 100% bonus is a decent deal, you should wait until the threshold is crossed of 4501 people buying before you buy yourself. Which means that everyone else should do the same. Which means that they’d never cross the threshold.

I see two possibilities for United actually giving out the bonus:

1. People are irrational. Remember, some people buy even without a bonus.
   
2. United gets generous. They award the bonus anyway, they run their science experiment but don’t want to stick it to customers willing to come out of pocket and buy their miles.

I wouldn’t be buying United miles at a 100% bonus speculatively of course, certainly not since they devalued.

Nice try, United. But this is why people don’t trust you. You take their money and say that you might give actual reasonable value, you’ll let everyone know later. Meh.

Terms and conditions:

To take advantage of this offer, you must use the order links on this page.

Promotional offer vaild until 11:59 p.m. CT (Chicago local time) on September 4, 2014.

Bonus miles will post to the MileagePlus account within 7 days.

For a limited time, get a minimum of 35% bonus award miles a maximum of 100% bonus award miles when you purchase miles via the above links.

Displayed price includes all taxes

Minimum purchase of 5,000 miles required for this promotion.

For Give Miles transactions, both purchased miles and bonus miles will be posted to the recipient’s mileagePlus account.

Miles are available in increments of 1,000 up to a maximum of 100,000 miles, and in increments of 5,000 up to a maximum of 150,000 miles.

Purchase up to 150,000 miles per account per calendar year.

Credit card will be billed immediately upon purchase.

Mileage rates and other applicable fees are subject to change.

Allow 48 hours for miles to process and post to your MileagePlus account.

Miles are nonrefundable.

Purchased miles do not count toward MileagePlus Premier® status.

All MileagePlus Program Rules and terms and conditions apply.

---

You can join the 40,000+ people who see these deals and analysis every day — sign up to receive posts by email (just one e-mail per day) or subscribe to the RSS feed. It’s free. You can also follow me on Twitter for the latest deals. Don’t miss out!