Can I use my laptop for another business using their Quickbooks account and software? (running two businesses from the same laptop)

Yes, you can have as many companies as you wish to pay for in the same device, ianjubb2. I've come to share insights and steps to help you manage multiple company files in QuickBooks Online.

If you have an existing Intuit account, you can utilize the same login credentials when signing up to the other QBO company file. Doing so will allow you to switch seamlessly between companies so you can manage everything efficiently. 

However, if you want these businesses to have separate sets of credentials, you can enter a new user or different user ID when logging in. To do this:

1. Go to the QuickBooks Online login website and click Use a different user ID/Account.
2. Enter the existing sign-in credentials of the other QuickBooks company file.
3. Then, select Sign in or continue.

Please know that these businesses are two different accounts, and all data entered from the other company file aren't automatically added or visible from the other business account. Thus, these companies are managed separately. You can also visit this article for more detailed information: Create or add another company file to QuickBooks Online.

Additionally, I've included this helpful resource to guide you if you want to use one user ID and move them all into one QBO account: Sign in to multiple QuickBooks Online companies with one user ID.

We're always ready to back you up if you have additional queries when managing your business accounts. Keep us posted in this thread, and we'll ensure to get you covered. Have a good one!