Need help valuing a property

[Luis Barahona]

Hello,

I've been sending mailers to homeowners in the area letting them know I'm interested in buying properties in the area. 

I've gotten responses from a few people. One owner who owns a duplex in San Francisco is interested in selling. We've met once to discuss my plans and I am touring the property soon.

I have comps for the property that I've gotten from a realtor friend. My question is how do I value the property? Is there a guide or someone that can walk me through this? Should I use the comparables approach or the income approach given it's going to be for rental income purposes?

Thanks,

Luis