Many US Attorneys have a threshold for initiating actions for Wire or Mail fraud that is much higher than the threshold in the statute. Five years ago (my last experience for a client who was a victim) the threshold was $70,000, though they will aggregate repeated scams to reach that limit and add in RICO counts. Many perpetrators are aware of this and avoid high dollar frauds.
Your best defense to such claims is:
1) deal with people you know, either a brick and mortar store, vendors with goods at a match or local fellow shooters;
2) if you buy via gun broker, armslist or a similar venue look at the reputation (avoid those with poor reps and those with few sales reps), check their address via on line satellite mapping services, look up their FFL status on line, look at the State Secretary of State's listing of business, especially if the State requires DBA listings;
3) never use pay pal, a check or cashier's check, send cash, wire funds, use prepaid gift cards, or debit cards - only rarely, preferably with someone you have a relationship with and/or checked out send a money order. Even if lost, it can take months for the USPS to issue you a refund, and you must pay for them to investigate. Use a credit (not debit) card. Federal Reserve regulations put the onus for preventing fraud on the credit card companies. The financial institutions approve who they allow to use their services. As a result you are protected from fraud. ONLY USE CREDIT CARDS NOT DEBIT CARDS - THEY ARE NOT THE SAME.
4) do not trust someone who suggests that they are a moral person because they go to church, advertise their Christian or religious beliefs or affiliations. Con men make their living by adopting the trappings of morality. (My client invested his companies 401K holdings with such a con man, referred by his pastor, who was also fleeced.) Do your research. Do not be fooled by a glib or truthful appearance; you will never hear someone say they were scammed by someone they did not trust;
5) run from any deal that is "too good to be true" - it likely is too good to be true and the lie will cost you;
6) most con men / scammers will try for a second bite, as reported by the original poster. This is a bright red, neon flashing warning sign, but it can also be an aid to getting your money back. If this should happen consider at that point hiring a professional to track the scammer. It is possible, but it will cost money, in most cases more than you are already out.
I wish the best. It is sad, but it makes us appreciate the overwhelming honest, fair folks in this sport all the more.