newbie here with 2 queations

[Emmanuel Gonzalez]

Hello I am very new to real estate investing. And by very new I mean this has been the first week I have ever looked into real estate investment. My first question is I have looked on Redfin and Zillow and seeing some house that look like they could have possibility to flip for decent profit. But I noticed that some of these have been listed for quite some time. What are some reasons that other investors have overlooked this property besides obvious things like major repairs?

My next question is what percent would you give someone who is only co-signing a property for you?