Annatvero on ebay

I recently won at auction on ebay several large ( over 10 ct) Faceted emeralds. They will arrive with a GIE CERTIFICATION from seller. He states they are Columbian SA stones .
How much faith can I put on a GIE Cert ? Also bought from separate seller 6 + ct Muzo Mine emerald ring. Where is the best place to send for appraisal should i secide to resale?

Buyer beware! I have seen (even bought) some very nice green quartz, quench cracked and dyed a nice green–sold as Columbian emerald with certification card. My GIA certified jeweler told me what it really was. Lucky I got my money back!!