Here are some reasons that come to mind as to why I have sent in coins or medals to a TPG company:
1) Namely to get some medal or coin authenticated if I have some amount of doubt that it may be real
2) For re-grade; if the coin is already in a slab from a second rate TPG but I want the coin in an NGC or PCGS slab
3) I believe the coin or medal I send in will grade in or near the top of all existing coins and medals of that type
4) If I have a coin or medal that I feel is 'valuable' (totally subjective term) but needs restoration, I will send it to NCS prior to sending to NGC
5) I have sent in an unusually odd sized modern 5 oz proof coin once that I purchased raw (came in no capsule) and no matter how much I searched, I could not find a capsule that would properly fit this coin....so I sent it in for grading and it came back in an awesome looking slab
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