How do I sell to merchants?

I found some Glitch merchants in town willing to sell me things, but I don't see an option or window to sell things. How do I convince them to take my useless things?

Solution 1:

As of 1.0 stable, most merchants have a 'sell' tab. You can drag your items or use shift click to add items to the sell list and see how much the items will sell for. Remember to click the sell button, otherwise the items will be returned to your inventory after the merchant's window is closed

Solution 2:

You cant yet. There will be an update (eventually) when you place the item you wish to sell on a block/crafting table like item and it gives you pixels.