We invested cash and took on traditional investor loans.I uncovered that there was a bit of cash out financing going on to free up money for more houses.... essentially pulling out all the created appreciation profit, and leveraging it to buy more new homes.

To which I spend hours at a time combing through the nitty gritty of homes until I uncover perfectly matched criteria "winners".

It's unfortunate that a buyer would have no other remedy apart from legal action in the above situation, but I agree it's unrealistic to expect inspectors or agents to perform heavy lifting / moving of furniture to uncover every last defect.

Does homedepot/lowes have these sort of things , or is it more specialised supplier ?

Sure it might be useful but he/she is not going to reveal any real goodies anyway; you need to uncover everything, the  good and bad, about the building and the finances for yourself.

In this case, I feel that if I am the one coordinating the repairs and fronting the capital to do so, as well as assuming risk of things not uncovered by a standard home inspection that may arise, then the price should be a fair bit lower.

The home inspection uncovered that the heat pump, a $5k replacement, was near the end of expected life.

But I learned that there is lots uncovered and I also wanted something that has more details.

Curious to know if other investors have had experiences where they acquired a property and realized a huge expense that they otherwise did not expect or uncover during due diligence?

That is entirely up to you if the offer you are making to the guy is a lot lower than you think he want I wouldn't even bother but a whole home inspection isn't a whole lot of money many people use the inspection to uncover latent deffects that you may not realize initialy if you could find a good handy man they may be able to point out what needs to be worked on and most contractors give free estimates I would do it that way but like you said at the same time the property must pass and inspection and appraise in the end if you are seeking conventional financing , I would find out if the guy is really motivated to sell first of all the inspection comes after you have a accepted offer not before .Goodluck