This creates high impact and visibility, though it can feel "loud" if used for more than a few words. Quick Style Tips

BUY & SELL DIRECT ONLINE

This is the standard for marketing headers. It makes each word feel important and intentional.

Which of these fits the on your website or ad where you plan to place it?

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.

Buy & sell direct online

Using the symbol is generally better for digital layouts because it saves space and creates a visual "anchor" between the two main actions. If the tone is very formal, use the word "and."