Scenario: I think I know some people that are selling their bikes. Let me ask around for you.
I reply back with:
What do these mean? Which one should I use?
1. You do? I think I know them too. I don't think they would want to sell their bikes.
2. You do? I think I know them too. I don't think they are going to sell their bikes.
Originally Posted by jack
 I think I know who you're talking about. Do you really think they'll want / are going to sell?
 I think I know who you mean. Do you think (if we ask them), they'd want to sell?
The second example houses a condition (if).