He probably should have mentioned the coins at customs.
Another easy way: There are coin dealers in Turkey. Just like in ANY country, there are coin-collectors who buy & sell. I just did a quick "yellow pages" type-search right now, and see several brick & mortar stores to-be-found in the bigger cities. Ok, if you bought something from one of them, the presto: lineage of existing , rather than "dug". I'm sure there's a buy-sell way to get a "receipt" for your stuff that you bought as souvenirs .
At one time I communicated with a seller located in Turkey, who had some ancient Turkish coins. I asked him if he could ship to the USA (posing as a potential bidder). He said "yes". Then .... playing the devil's advocate ... I asked "isn't there laws to forbid ancient coins from leaving the borders?" He said that as long as their "souvenirs", (and you're not "digging" them) them, then in that case, trinkets (aka souvenirs) come and go through the mail no problem.
I posted this Turkish coin-seller exchange on an old T'net thread on the subject of Turkey, and was told that the coins I was looking at are no doubt "replicas". And that *if* they were truly old coins, then the seller was mistaken. Ok, then what's so hard about having a coin-dealer write you a writ stating "replicas" , for in case anyone cares to scrutinize your luggage ?
Who knows ? I just know that a buddy of mine, walking the streets of Istanbul, saw a Whites dealer logo decal in the window of a shop. He peaked his head in the door and saw a few detectors on the wall. Thus locals can indeed buy detectors. Presumably for legal purposes. I suppose the argument could then be made that "yeah but you can't leave the country with anything" ? The debate would be endless.