Your question is how you can identify a high quality solar panel. The truth is that you can hardly detect a poor quality panel by merely looking at it.
The first thing is to make sure you buy a reputable brand panel. buy a brand that people trust. Go through the specifications yourself and check the panel efficiency and power output.
You may not have the time to use your multimeter to confirm the power output but just stick to a brand that people trust.
Also make sure you buy from an authorised dealer of the brand.
Last but not the least, try to inspect the cells of the panel and make sure the cells are all of uniform colour. Good luck.