How to add finance charges and payment terms to an account sale

Find or create the account sale

While on the account sale screen select manage account
Select account options.
In the payment terms fieldselect the terms from the drop down list. 
If you are charging finance, next to finance charge select yes and enter in the percentage
If you want to place a limit on the account, enter that amount in the account limit field.
Selet save changes.
 
Note
You can set up the default payment terms and account limit for all account sales by going to utilities, sales, account sales.
These defaults once set up will apply for all new account sales.
You can then override the default by using the steps above.