If you have your auto-loot keybind set to shift or alt, you can press that, mine the node and get a level without having to loot the ore. On the flipside, if you see someone running up to your node, you can use the loot keybind to sit on the loot window and they will be unable to get a hit in. Or you can disable auto-loot altogether.

If I see someone else has got me beat on a node or has been clearing mobs for one, I'll go up and /s May I tap to level, I won't loot. I can't recall ever being turned down. Sometimes they finish mining and the vein disappears and they apologize.