Low-ball offer or move on?

[Daniel Walker]

To those who are experienced in buying long-term rentals--

When making an offer on an MLS-listed house, if the numbers really don't make sense, is it best to make a low-ball offer or move on to analyzing the next potential property?

Is there a point at which low-ball offers are simply counter-productive to time and reputation?  If so, what is that threshold--20% off the list price?