This is the standard for marketing headers. It makes each word feel important and intentional.
BUY & SELL DIRECT ONLINE
Which of these fits the on your website or ad where you plan to place it? buy & sell direct online
You do not need a hyphen between "Direct" and "Online" unless they are modifying a noun (e.g., "A direct-online marketplace"), but for a general call to action, keep them separate. This is the standard for marketing headers
This creates high impact and visibility, though it can feel "loud" if used for more than a few words. Quick Style Tips "A direct-online marketplace")