Hi JPW,
Welcome to Method and the Method Forums! First off, I am not sure you came across this article in our Knowledge Base, but it should shed some light on what happens when you actually delete a Customer in Method or your QBO account. Long story short, it describes that QBO doesn't fully delete Customers, they make them "Inactive", so they are still somewhere in the database, but unless you show "inactive" Customers, they won't show up in any of your Customer List. I also came across this Method forum post which explains how to filter out unused Customers in Method if you don't make them inactive.
If you find that you want to make all these Customers in question "inactive", you could do with more than one record at a time. I would suggest creating a new screen based off the Customer table, then add a grid based off the Customer table to the new screen. Add whatever columns you require to identify the Customers you want to be made inactive, of course make sure to include the "isActive" field. That is it for this method, now load your screen uncheck each Customer you want to be made inactive, from the inactive field, then press the Update button. If you still find this method cumbersome because you have too many records, there is one other option with this setup you could try. Instead of checking off the isActive field and pressing "Update" for each grid page, you could create your own button at the bottom, label it "Make Inactive". For the actions on this button, first start looping through the grid, check off option "only checked rows", so you will only make the rows of Customers you have checked off. Then add the action "Update Field in Table" and make the logic so if the isActive field is Active(TRUE), then make the field FALSE. Keep in mind for this second approach, you will need to make sure the "checkbox column" option is selected in your grid. I have attached a screenshot below of a quick and dirty example of what this might look like:
-Ben