After many years, I have my own methods, resources and abilities and I have enjoyed much success.  

There are a number of strategies out there but one I often hear about doing well is the BRRRR method where you Buy Renovate Rent Refinance and Repeat it creates equity and cash flow for you at the same time while also allowing you to invest in better neighborhoods which have better tenants in which you can safely scale up and expand your portfolio But ultimately the deal is in the numbers so the better you are at analyzing deals the easier it will be for you know when you have found a good deal so practice analyzing as much as you can to sharpen your skills because even as a wholesaler your deal analyzing skills must be up to par because your selling your deals to investors who do this on a regular basis hope this helps 

Other methods, like relying on a cellular data connection, might prove to be cost prohibitive.

Should I just send a letter to the abandoned house's address and hope the owner eventually stops by or are there other methods for tracking down owners?

3 accepted methods of valuation:comparable salesreplacement costvaluation based on income

You will most likely pay the same amount to have the attorney set it up as you would one of the other methods. 

How has their method worked out for them?  

Clearly a background check is the best method to avoid a bad renter but do you know what should be in the report and how to get it?

I'd like to own the property & lease not a short sale.Are there alternative methods just in case lenders or investors may not be an option?

It also means you should be targeting houses that need very little work, to avoid putting money in the deal.I do not like this method of investing as a primary business strategy.