One of my biggest red flags when dealing with lenders is lack of transparency around fees.

Is having a ton of rental properties & installment sales in a massive 1040 tax return - an IRS audit flag??

If the prospect puts up a big wall and is dismissive about their record, that is more of a red flag than the record itself, but if they were straight forward and honest with me, I will know I can trust them.

Its one thing to have an opinion, but I would not want biggerpockets to have a chatbot to answer those questions (nor would I assume they want the liability).Within your comment lies the more reason for AI powered fact-checkers and flagging system that can flag bad and good advice.

Any red flags? 

On the other hand if they are a sponsor that is experienced in stopping a skin in the game, that's a huge red flag for me.c) how open to scrutiny are they?

If your lender is only working with a "list of qualified contractors" thats against the 203k guidelines and a huge red flag. 

What are some red flags ?

That raises a ton of red flags to me.

Also remember the time these returns will take to amend along with the possibility of opening up audit periods/red flags with the IRS due to amendments.Doing this yourself on turbo tax likely won't be your best bet considering all of the details.