Assessing the quality of a knife can be challenging without detailed information about its origin and materials. However, there are some general indicators you can use to get a sense of its quality:
Sharpness: As you've already done, checking the sharpness of the blade is a good starting point. A high-quality knife should be able to achieve and maintain a sharp edge with relative ease.
Edge Retention: A good knife will hold its sharpness for a reasonable amount of time, even with regular use. If the blade quickly becomes dull after minimal use, it might indicate lower-quality steel.
Balance: A well-made knife will have a good balance between the blade and the handle. It should feel comfortable and easy to control in your hand.
Weight: Quality knives tend to have a certain heft to them, which can vary depending on the type of knife. Generally, heavier knives made of good materials may perform better and require less effort during cutting tasks.
Handle Construction: The handle should be securely attached to the blade, with no signs of gaps or loose fittings. A high-quality handle material, such as durable wood or synthetic material, is also a positive sign.
Steel Thickness and Flexibility: A 3mm thick blade is quite substantial, which could be a sign of durability, especially for heavy-duty tasks. The flexibility of the blade should be appropriate for its intended use; some knives need to be rigid for precise cutting, while others require some flexibility for filleting and deboning.
Corrosion Resistance: If the blade is made of stainless steel or has been treated to resist corrosion, it's more likely to be of higher quality.
Keep in mind that even a cheap knife can be sharpened to a razor edge with enough effort on a whetstone. However, the true test of a knife's quality lies in its ability to maintain that sharpness and its overall performance over time. Some lower-quality knives might not hold up well under regular use and may lose their edge quickly.
As you mentioned these are handmade knives from Iran, they might have unique designs or craftsmanship, and their value may not necessarily be determined solely by the materials used. If you are satisfied with the knife's performance, then that's what matters most. Just remember to take proper care of the knife, honing and sharpening it regularly, and handwashing it to maintain its performance and lifespan.