What is an OTO?
Internet Marketing Dictionary | OTO - One Time Offer

An OTO or one time offer is a method of increasing sales by offering customers a special deal that is only made available to them once. For example, you could make a one time offer of a massive discount on an ebook to new subscribers to a newsletter.

An important feature of a one time offer is that its limited availability is made absolutely clear to the customer. If it isn't made clear it won't work.

The psychology behind OTOs is that you know that you will never get such a good deal presented to you again and if the value of the deal exceeds the price the conversion rate can be very high.

Many internet marketers use one time offers, especially as up sells, but in a lot of cases that statement that the offer is "one time and one time only" is actually false. Simply reloading the page having deleted cookies can often bring an expired one time offer back again.