When creating a SlyBroadcast message, you want to be somewhat general and also  be specific so that you can filter out people from calling you back that are not interested in selling their house to you. Below is an outline of SlyBroadcast messages that you can use.

Hey, how's it goin'? We spoke about your property in the past, if you're still interested in selling please give me a call, if not you can ignore this message. Our company just came across more funding and are looking to purchase a few more homes this week."

Pro tip: 

Audio file size should be less than 10mb
Once a sly-broadcast campaign encounters a file related error like too big or too long, all the other file that you upload under that campaign will have errors. So new file means new campaign, create a new broadcast each time you want to try a different file.