A bonus week can be given at a presentation or from a trading company trying to entice you to either buy a timeshare at a presentation or trade with a certain exchange company.
When purchasing at a presentation, the agent may try to “sweeten the deal” by throwing in some extra weeks of vacation. This is used to try and entice their clients into buying right then and there. Since most presentations will only have you there for a few hours at most, so it’s there job to put the pressure on and not let you walk out without buying.
Another case where you may be offered a bonus week is when trading. The exchange company may incentivize your membership by offering a bonus week out of their exchange inventory. This is decidedly less common than bonus weeks given at a presentation.
In some cases, bonus week packages that are given as incentives can require a fee to use, and/or may not be for the resort that was purchased. Read all offers thoroughly.