This is a common problem, especially with large fundraising drives where one person is entering in a lot of donations on one computer. Whenever an interaction is made with our site and the constituent is new to our system, a contact record is created for them. Out of convenience to the constituent, by default whenever someone is automatically registered in this context they will be logged in. This can cause a lot of issues with donation drives, as if a constituent is logged in, even if their billing information is different from their contact information the donation will be attributed to their record. There are several solutions to this problem:
  1. Enter the transactions as offline donations - This is really only an option if you have a relatively small number of people to which you are comfortable giving Administrator access
  2. Add a logout link on the thank you page of the donation form and instruct those entering the donations to logout after completing a transaction. 
  3. Disable the functionality that logs in users who have been automatically registered. Note that this will affect all new constituents in every context that will in which a constituent record is created. The site option for this is called "CONS_AUTOREG_LOGIN." An Advanced Site Administrator may be able to change this value but if they cannot see this option under Setup > Site Options, please contact support and reference this article number.