Obtaining a certificate of authenticity is a good thing. However, a certificate of authenticity comes at a cost. The minimum cost (as of this writing) is about $20. The cost is higher for more valuable items.
Sometimes the decision to get a certificate is easy to make. For example, suppose I have a copy of Scott #245 and I want to know if it’s regummed or not. Assuming the stamp isn’t a fake, either way the stamp has substantial value. Spending $20 or so on a certificate is an easy decision. When I sell the stamp, I can get back the cost of the certificate.
Sometimes the decision to get a certificate is not so easy. There is a risk that you never get your money back. This happened to me very early in my career as a stamp dealer.
I had a copy of what I thought was Scott #500. I sent it to APEX and it came back as Scott #499. Rats! I just spent $20 to find out that I have a 20¢ stamp! I can never ask for $20 for this stamp, even with a certificate on it. As a dealer, I have to eat that loss and learn from that lesson.
As a collector, you face the same dilemma. Suppose you find a stamp and you’re not sure if it’s the valuable variety or the common variety. Are you going to spend $20 or more on a certificate and hope it’s the valuable variety? If it comes back as the common stamp; that is money you’ll never get back.
Unfortunately, there is no crystal ball that can tell you, “Yes, get the certificate,” or, “No, It’s common. Don’t waste your money.”
One thing you could try is to show the item to one or more people whom you trust. Maybe there is a person in the local stamp club who is very knowledgeable about stamps. What do they think? If you ask two or three people and they think you have something valuable, maybe it’s worth the risk spending the money to find out if you really do have something valuable. If two or three people don’t think it’s valuable, maybe you want to think hard before spending the money to get a certificate.