need help please

back in june my cousin and i opened up a ebay account. we sold my collection of Magic the gathering trading cards. this is a small card game that has become a collectable. included in the 50,000 cards were a few of the higher valued cards. the collection was sold for 2400.00 . the person paid via check that was made out to my cousin as it was her account. the buyer requested the cards be sent to his "partner". i have thie email. several weeks after the cards were shipped from my works shipping department (which i did to make sure i had a record of shipment) the buyer took the collection to the local police department and claimed that the cards promised were not in the lot shipped by us. also as is common place for this game we had a few(5-6) "proxie" cards in a deck of the cards that was included . these are commonly photocopies of the real cards to be used in the decks so the real cards sometimes valued at 250-500.00 each dont get damaged from usage. i can have statments from all 15 of the los angeles aria dealers in these cards attest to this common practice as it is even recognised by the game manufacturer. these were made very obvious as no one who plays the game could possibly mistake them for the real cards.

the detective called up my cousin. telling her that she had to give back the money she collected for the collection or be arrested for counterfitting and theft. he was verbally abusive and would not listen to anything she said.

we contacted a detective out where we live and explained the situation to him and he laughed and stated that this was completely a civil matter and that we "shouldnt worry" but also to tell the detective that we would cooperate with the investigation.

we contacted the detective and was hung up on after being berated by the detective telling us he didnt want to listen to what we had to say.

we contacted his superior officer, explained the situation and told him we would be more then happy to assist in the investigation.

3 months later after no contact with the detective he calls again. this time again using the same abusive tone and the threats of theft charges and placing a warrant out for her arrest. again we try to discuss this with him and he refuses. we call the same superior officer and this time he basicly give the same additude that the other officer gave as he hung up on us.

2 days later he calls and says that she had till that following friday to send the money or have the warrant issued out for her arrest.

its now wednesday after the threat, we have contacted a lawyer.

she has left 7 messages for the detective cince he gave the ultimatum and so far have not recieved a single responce from him.

i am just confused as to how this could be even considered a criminal matter.

1. he waited several weeks before filing a complaint.
2. what proof does he have that the cards were not in the package when it arrived(which im sure it was as they WERE packed)
3. no contact was made by the buyer to either of us prior to filing this complaint. not even a email.
4. the detective claimed that none of the high valued cards were in the auction, there was over 120 cards that were listed in the auction description none of these cards but conveniently the 5-6 proxies are said to be in the collection. the 2 folders and the 3 deck boxes included in the collection were not presented to the officers.

what do we do? is there anything we can do? is there a basis to sue the police department? any help will be apreciated.