I agree with Tina and Ron. If you have "Buyer's Remorse" and you no longer believe it is a good investment, your best option is to get out.
Unless you find some serious issue with the property, (e.g. structural damage - in which case you do not want it anyway), you probably will not be able to get seller to reduce by 15%. Just cancel the deal during the 7 days inspection period. Usually, the seller will let you have your earnest money back. Next time, you may wish to contact a good realtor, who will do the research and due diligence for you.
How do you know this?
If you BELIEVED this, and acted on it, how you find fault with anything anyone else did?
Here's the short story about LISTING PRICE:
Understand that the LISTING PRICE has one primary objective, to attract attention: It is not intended to be set in stone, and in many cases it is not even a good guideline toward the SELLING PRICE.
Some Sellers believe that by setting the LISTING PRICE high, they can always come down, and people will make an offer anyway: WRONG! Buyers will just bypass the property and look at houses that are within their price range. And six months from now, the Seller will slowly start lowering the PRICE, (this is called “chasing the curve”) and Buyers will be asking the question; “What’s wrong with that house?” and “Why has it been on the Market so long?”
Other Sellers set the LISTING PRICE low, to attract multiple offers. (The correct strategy.) We are asked; “Aren’t you obligated to sell at this price if someone offers it?” The answer is probably not; for that to happen, you would first have to have only one offer, and secondly, the offer would have be exactly the same, down to the smallest detail, (please discuss this with your Realtor).
Another thought; Buyer will search for potential properties by groups; for example, $400,000 to $450,000, and $250,000 to $300,000. If your house is priced at $460,000 or $310,000, the Buyers will never see it. (something else to discuss with your Agent.)
Different Banks have different philosophies about pricing their properties: You cannot draw any conclusions without a good analysis.
Have your Realtor do a CMA, (Comparative Market Analysis) to help you determine your Offering Price. It is the surest way to determine the Market Value of the property.
As far as Multiple Offers goes; have you ever met a Used Car salesman who said something like this>
And, honestly, you didn't act because of the Multiple Offer tip.
You saw GREEN and you did what you did; no one coersed you. You cannot blame anyone else. You chose to move without a CMA nor an Appraisal, you chose to offer cash, if you offered more than Market, Caviate Emptor.
Good luck and may God bless
These questions need to be directed to your Realtor. If you're working with a competent investment real estate broker, you'll know exactly what you're doing and why.
A winning bid is by definition an overbid. As for any credit, that's not possible at this point. A deal is a deal.
Your own option at this point is to back out if you are truly concerned that you have a poor deal in your hands.