If I call the seller directly, is it taboo to start asking for financials or should I just ask if I can send them an LOI?   

I have a "friend" that has an apartment unit that consistently has bad tenants.

Either market will take time to stabilize and have challenges to overcome, consider which one you can manage easier an balance that with your ROI. 

An Eagle hunts alone.

I was going to run an STR in the home and he would enjoy a higher rent than from a regular LTR rental AND he would have the property managed too.All was going beautifully.

I believe it's important to understand there are certainly examples of investors who succeed with the use of the section 8 rental program but there is generally an underlying thesis that leads to the success, not the section 8 program or "guaranteed rent"  in itself.

I am an investor and Realtor now in DFW area.

We bought an extra ticket and room for a guest and now they are not able to make it.

@Fernando GuzmanFirst thing is to pick an investment and stick with it.  

Shouldn't be an issue in most big cities having a list of cash buyers that are just dreaming you will bring them a 70%-repair deals.