offer - contingent on their house sale
Okay, I've never sold a house before. Our agent called and there's an offer, but it's contingent on the buyers selling their house. (I don't really know any other details, because the agent wants to meet in person to discuss, won't give us anything else on the phone.) She called at 9:30 at night to tell us, so we're meeting her tomorrow evening to review the offer and make our counter (which she says we should do).
How does this work with a contingency like this? I'm not crazy about sitting around for weeks/months waiting for someone else's house to sell. It's stressful enough waiting for our own to sell. What do we look for, ask for, what are our options, etc.?
On the bright side, the house went on the market officially the day after Christmas, with the holidays we didn't have any activity until after new years. We've had only two showings, and now an offer, so we're really encouraged by that.
Any advice or explanations of how this works is appreciated.