Do you know who is a professional hunter and who is an amateur? Anyone, even being far from our hobby, will be able to answer this question.
It doesn’t matter what experience you have or how much your detector costs. Someone who earns by his hobby is a professional. Someone who simply spends time with pleasure is an amateur.
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In case of searching old archeological stuff, someone who only search for the finds (or worse, profit) is an amateur.
Someone who is searching to learn about the history, shares his finds to the public and works together with archeologists is a pro.