Once you've added the contact and selected the type "Supplier/Manufacturer," please do the following:
Mark the account as Trade or Retail.
Enter your Designer Discount
Enter your client Mark-up.

Now, when you've added the item from that site and you notice that they're not auto-populating; please make sure that you select the "MFG" field so it will populate.
If you only selected the Supplier, the discount and mark-up will not populate since these are connected to the "MFG" field in an item.
In the example below, the MFG field has been selected via the Clipper tool.

Here is a sample when adding items manually:

Once you add a new item and then set the "MFG" field, the discount and mark-up will auto-populate.
*Note: Setting the discount and mark-up in your Contacts list will not auto-populate existing items, only new ones you add forward.