What are things that you wished you had found out about prospective tenants, before approving them?

These niches mentioned have solid historical records of performance and good future prospects due to various demographic trends.  

I listened to several podcast, I cant just single one out but just wanted to get different a prospective from the people I want to be like.

You will offer a contract of sale where there would be no commission or settlement cost and that your offer is NET to seller.Once you have control you can now work on locating an assignee - you have options -List it - not a great option -  if you want a fast sale -listing it will take too long - too many contingencies - too many gate keepers.Offer it privately for sale - all cash - as is - social media - too many moving parts - you need to negotiate with prospective buyers, show the property - write a contract of sale - and demand CASH - won't be easy - My favorite option (remember I am an auctioneer) - offer the property - while in contract - at PUBLIC AUCTION - advertise it for 3 weeks and let the auctioneer do his magic - it is fast - predictable - all cash and as is without contingencies. 

I've not always had an agent representing me.Given that, what are the pitfalls, if any, in this prospective deal if there's technically no selling agent involved and i don't bring an agent to the table representing me?

To stand out, you have to go the extra mile and do more than just send thousands of emails and direct mail pieces to all prospective sellers.Direct mail advertisingDirect mail advertising is one of the most effective forms of advertising.

Would a yellow letter campaign be appropriate for trying to find a deal to these prospective type of sellers?  

I am looking for views from the professionals and non-professionals in the D.C. area on looming changes in the investment prospectives with the new Trump administration.

Spent money and time on marketing and prospecting but no results.

It seems as if your prospective landlord wants to have unreported income and the ability to easily evict you if a purchaser requests vacant possession.