Offer price in a buyer's market

[N/A N/A]

We're newbies...go easy! :D

We're about to buy our first investment property, a duplex with excellent income. It has been on the market for 200+ days.

We're making an offer soon. Is there a rule-of-thumb for the initial offering price?

The seller is selling off some of his numerous properties in the area, so we're not sure how motivated he is.

Thanks for any input.