After following the right dialogue tree, the player will be able to sell Vault jumpsuits to Sarah. She will accept jumpsuits from any of the in-game vaults other than Vault 21. With a Barter check of 65, she will accept Boomer jumpsuits and Boomer flightsuits. Vault 3 suits can also be bought at Mick & Ralph's, but they will only have 1-4 suits, and once you've purchased them they do not restock.
Vault 3 and Vault 11 both have large numbers of jumpsuits in dressers in their living quarters (24 & 28 respectively). See Vault jumpsuit for more locations.
You will receive caps, Strip reputation, and a discount on the Vault 21 guest room. After you bring her 30 Vault suits, she'll mention that she's missed you when you visit her next. You will then be able to have sex with her as you both "catch up" with one another in your room, which gives the Well Rested bonus (which is normally not earned by sleeping in Vault 21's guest room). Also, after two Speech checks, 65 and 75 respectively, she will agree to have sex after receiving suits, along with accepting Boomer suits.
Sarah only accepts vault jumpsuits from Vaults 3, 11, 19, 22, and 34. Notably, she will not accept any suits from Vault 21 itself.
Giving Sarah one jumpsuit at a time results in more Strip fame than giving all 30 suits at once.
For the first visit Sarah will accept 10 suit offers in succession. After this initial 10 offers in succession, Sarah will accept suits once every 24 in-game hours.
There is no limit to how many times the player can sleep with Sarah for the Well Rested bonus, but in hardcore mode, it does not lower the sleep meter, and simply passes time. This makes it necessary to rest normally in one of the beds, which also passes time, leading to dehydration and starvation. For this reason, sleeping with her simply for the bonus in hardcore mode is very inefficient. It's better just to find a bed that addresses both SLP and well rested.
Although Sarah can be convinced to accept Boomer clothing, giving her these items will not count towards the total number of vault jumpsuits that must given her in order to have sex with her.
A high Perception (8+) may be needed to start the conversation that leads to asking her about the suits.
If the character is female, the two speech checks will not show up, even after the quest has been completed. Renting a room is not required prior to having sex with Sarah. The game will simply recognize that the quest has been completed and the option to have sex with her will be automatic.
pcps3xbox360 The player will gain the same amount of Strip fame each time they turn in vault suits, regardless of how many vault suits are turned in at once.
pcps3xbox360 Sarah will sometimes use a deeper female voice upon greeting you or after finishing a trade. [verified]
xbox360 Sarah will sometimes take Vault 34 suits, but won't accept Vault 22 suits. [verified]
pcxbox360 If the player leaves the vault after giving Sarah the 30 jumpsuits and she agrees to sex, without first having sex with Sarah, she will remain in the gift shop and it becomes impossible to interact with her. [verified]
pcps3xbox360 Suits held by the Courier are counted twice: once upon entering the gift shop, and a second time when first speaking to Sarah. However, some of Sarah's greetings do not do this second count, making it possible for the Courier to arrive with a large number of vault suits and/or Boomer outfits, drop or transfer all of the clothing, then engage Sarah in conversation and redeem the reward without actually turning in any clothing. Because only specific greetings are affected, this is only possible if the player has not turned in more than 30 suits total, including "phantom" suits turned in via this bug but not including any Boomer outfits. [verified]
The specific greetings affected are the greeting that starts with, "Well, well! If it isn't the Vault explorer..." which occurs after giving her between 10 an 30 suits total, as well as the "Behave..." greeting which only is seen if you have turned in less than 10 suits total and have angered Sarah in conversation.
pcps3xbox360 The above bug also works in the opposite direction: if the player takes vault suits from a companion's inventory after arriving at Vault 21, the additional suits will not be counted towards the total turned in. However, the additional suits will not be removed from the player's inventory either. Leaving the gift shop and then returning will allow the player to turn in the remaining vault suits. [verified]
Note that the player must only leave the gift shop rather than Vault 21 entirely, as the two triggers which recount the Courier's vault jumpsuits are placed in front of either entrance to the gift shop. Simply walking partway down the stairs and then back up again will recount the number of vault suits the player is carrying.
pcps3xbox360 With Veronica as a companion Sarah will come to the room to have sex but then leave before and the player will be stuck. [verified]