Suspicion is one thing, proof is another. If you intend to pursue this, you're going to need an attorney who will review your offer, what proof you have and where you might be damaged.
A seller can choose whatever offer they want provided they don't discriminate on the basis of a protected class. If you are a member of a protected group, you may have a case, if not you may be out of luck.
If the seller has a valid business reason to accept another offer, you may be out of luck. The highest price offer doesn't always win. Sometimes a buyer waives contingencies that you may not have, or has a larger down payment, more secure loan pre-approval letter.
Let us know what you find out.