Q: How, do I check my default selling price formula? How to include supplier shipping cost into my formula?
A: You can find out if your items have override formulas or not (meaning they would not be using your default formula) by exporting a CSV from Sku Grid (Import/Export --> Export CSV) and in the Selling Formula column, if you see any formula or values there, that would mean that the items have an override formula.
Next, you can check your default formula by going to Settings --> Marketplaces --> eBay --> Country and click on the switch to wizard view button to look at the formula you're using.
Be sure your margin is the one you would like for your items, and check out the other fields. You can change it there. You can or not Include Supplier Shipping in Calculations (This is according to your needs). Once you've changed this formula, click Close & Apply. Then Save Settings.
If you had override formulas on any of your items, you can remove all overrides at one time, by going to Batch Options --> Remove All Per Item Formulas.
Then force all items to update by going to Batch Options --> Force All Items to Update to push them all through with your new formula.