Ask her to... clarify...

"Hmm..." you humm to yourself, eyes wandering over the girl's body. "How old are you, Fiona?"

"Twenty," her eyes locked yours, both fearful and hopeful at the same time. Her chest heaved slightly higher

So, she was plenty old enough then. Only a couple of years younger than yourself, actually.

"Well, I'd like to accept your offer..." you drawl, shuffling forward slowly, sliding your hand up the spear as you went so that you didn't accidentally poke her. "But how do I know you won't just knock me over the head when I get the jewels? Or run away when you find out what I think 'keeping my bed warm' means."

"I know what it means," she said flatly, eyes trained on the hand as it was sliding up the spear. One wrong move, and, despite the awkward position on the shaft, you could still stick her with the pointy end should she try anything funny.

"I'll prove it."

That was what you were hoping for.

With a grin, you withdraw your spear slightly, holding it off to one side to allow her to approach.

Hesitantly, Fiona pushes herself off the wall, and walks over to you, both suddenly tense.

If she was going to try to escape, then this would be the time; when your spear was out of the way, and you were awkwardly positioned.