How buying a TikTok username works
A TikTok username usually comes as its own account, with the name already on it. That means there's no swap window for snipers. TikTok also limits how often you can change a username (about once every 30 days at the time of writing), so receiving the account with the name in place is the simplest route.
Read what's different about TikTok and Snapchat usernames for the details.