Hi Darrin,
You cannot completely delete a customer from the Method database without also deleting it in Quickbooks. However, you can clean up the clutter in your Method account. One way to do this is to filter your grids to not include any customers with the CustomerType field labelled 'retail'. Let's start with the Customers and Contacts List tab link. If you click the Filter By View setting near the top of the grid, you have a choice of some preset filter views. If you wish, you may customize this screen to include more of your own filter views (e.g. one that filters out 'retail' customers). Is this something that interests you?
A second solution could be to make these customers inactive, however this will sync with Quickbooks and cause them to be inactive there too.
If you're interested in starting with filter views, I suggest watching our webinar called Introduction to Method Objects - Level 1. You can find it here in the Customization section.
Let me know if you need any help with this or have any more questions.
Jason