Address any maintenance issues they have. 2.

My tenant has vacated (she had till end of May to complete her 12 months lease) the property without notification (no final walk thru) and no forwarding address.

Some of these CapEx items might have to be addressed as rehab in your initial purchase. https://www.biggerpockets.com/blog/2015-10-13-real-estate-capex-estimate-capital-expenditures

When I find a property I'm interested in, I select it, and I'll click the button "Click for complete address" it takes me to a page to put in my credit card info.

Your tenant can probably look you up in public records as the owner and get your address from there.How do you plan to do in-person management? 

Not sure how to address your question without basic info.  

I cringe every time I give my address over the phone to someone and they say “can you please repeat that?”

I have shared the obvious answer that he would take the the house back, but I can tell he is still worried about having to foreclose.What techniques or messaging do you find effective to address these type concerns and put the seller at ease when trying to close a seller financed deal?

This makes sense to me for two main reasons:  I think there would be a single tap fee to tie into the main sewer line and spreading the costs out over time.I'm sure there are variables I'm not addressing, so please let me know what I'm not thinking about yet. 

The thing is I cannot get the owner contact info or new address in the county tax records.