Consider working with a list broker rather than a "website" to get your seller leads.

I just had to have a contractor take a "lead certification" class yesterday as he was not aware the bank will ask for that certification. 

All this does is tell the lead who you are and why you are calling.

The other potential downside I've had someone bring up is that when I go to get a loan to do another rental property it will look bad on me as a property manager and investor because I have a property with negative cash flow leading the bank to believe I am incapable of managing properties and likely to default on my loan.

I've decided that direct mail marketing isn't yielding the results I need and I've decided I want to skip trace my pre-foreclosure leads and call them directly.

Personally, I think it will just lead to a hassle down the road, and landlord/tenant relationships should (in my opinion) always be nothing but business. 

“Ultimately, Zillow Instant Offers has the potential to deliver the highest intent, highest quality listing leads at scale to our Premier Agents.” - https://www.geekwire.com/2018/zillow-group-will-st...KH

In wholesaling, if a real estate agent gives you a lead on a house and you end up putting it under contract and successfully assigning it to an end buyer, is it legal to give the real estate agent a percentage of the assignment fee?

If your plan of flipping homes leads you to your "Critical Mass" point, then by all means execute on your vision vigorously. 

This should save me money on my own future deals, while also helping me gain credibility within the industry and my local area as a serious real estate investor and deal maker.As for my professional background, I have been working as a freelance social media marketing strategist for 7+ years helping B2B companies generate and nurture high-quality leads on LinkedIn.