Calculating ARV, Inventory Levels, and Comps

[Samori Diallo]

Hello,

I am currently in my education phase, soon becoming a wholesaler. Can someone please clarify the following for me:

1. I see a lot of people explaining their calculation methods for ARV without inspecting the physical condition of the properties. How accurate can an arv analysis be without going out and seeing the home yourself or sending a trusted inspector?
2. How does one go about finding out what the inventory levels and sub-categories are in a target market? Do we get this information from Real estate agents, checking the mls, or by some other means.
3. Lastly, how does one learn to make the adjustments when doing comps for homes that are not exactly the same makeup? Is it something you learn over time from doing it, or is there training on that anywhere? I believe that is a crucial skill to master. (ex. 3br 2bt and a 5br 3 bt) Thanks! I look forward to reading the replies.