Riddle of the week - The Case of the Archaeological Dig

"I've finally earned my place as assistant curator of the museum", said Bob Hobbie to Max, the chief administrator of the Belgra Archeological Museum. "I moved West of the Pakistani dig site and we've just unearthed some wonderful coin artifacts."
"Why did you start digging in a new location?" asked Max.
"One of the local natives told me that, for many generations, his family had passed down a legend of a lost village and he found a map among his father's things," said Bob. "His father recently passed away", he added. "The native followed the map and led me to this site on the condition that if we discovered anything of value he would be paid one thousand dollars", explained Bob.
"And what is it that you found buried,?" asked Max.
"It's just terrific," exclaimed Bob, "we found 3 gold coins of various sizes dated 400 B.C., and after properly dusting them off I found them to be in excellent condition." "I quickly paid the native to complete our verbal contract and keep him from trying to claim a portion of the discovery," concluded Bob. After considering for a few moments, Max told Bob that when he returns home he should look for another job!! Why?