“I’m busy right now. I’ll call you back.”
They may be busy or suspicious. Try to get a small commitment here – ask if they can answer 1 quick question in less than 1 minute. This will set you up for further conversations later, where you can offer more detailed help.
I totally get it, If I could just ask you two quick questions I can have you off the phone in less than 1 minute. Would that work?
1) Are you still thinking of buying or selling?
2) When could we schedule a call so you and I can chat in detail?