What parameters should I consider to make sure about the high quality of power tools?

By Alan Chenkin, Trained as a Machinist/Mechanic in the NYC schools, Life long Mr. Fixit
When you buy power tools, with all the choices today, it is almost always better to purchase a well-made tool. It will perform better and usually last longer.
If we look at drills, some are inexpensive “homeowner grade”, have chucks that wobble, and may be uncomfortable to use. Others are sleek, well machined, and powerful. Both grades of tools will do the job, but the better grade tool will give you better results over time.  Always try to use the tool before you buy it, to make sure it is good for your purposes.
In addition to the look and feel, read the reviews. Most people will give an honest opinion of their equipment, and it gives you a basis to go on. Many sites have reviews of tools, comparing several brands and picking a “best of” choice.
In the case of table saws, there are many inexpensive choices, and the specs are published and well known; It is as important to set up the saw properly (link to Amazon Books) and use the correct blade for the work as the make and model of saw. Of course, if you start with a better saw – Altendorf, Martin, Jet, Powermatic, Grizzly, etc (link to Amazon tools)., And you set it up properly, it will be a wonderfully good machine to use.
There are other considerations as well. With battery tools, you may want to stay with one brand – This limits you to that line of tool, or you may have to have multiple brands of batteries and chargers on hand. Here you can pick the best compromise between quality, function, and standardization.  This is a list of Battery tool kits from Amazon.  Kits give you the best value, and multiple tools.
This is a Black and Decker 18 Volt drill kit. This kit has a good buy for a homeowner or casual user for about $80 USD. IF you need tools, and it’s not your day job, this is a good buy.
Here is a DeWalt 18 volt drill for $122. You will see tradesman and professionals using this drill, which is heavier than the Black and Decker, has a more powerful motor, impact resistant plastic case and fast charger. 
Both of these drills do the same operations, but if you place them both by side, you will recognize the feel of the “better” tool, with its higher price tag, better bearings and power.
If you are presented with choices, you can always ask/write me directly, or send me some tools to test for you! (hope you find this funny, but I would graciously test any tools given and freely blog about it)! (shameless self promotion).
Check the return policy for your tools, so you can return them to the store if they are not the quality you are expecting. Tool purchases are not everyday occurrences, so take your time and make sure you are getting a good product for your money. Also check the warranty, so if it wears out prematurely, you have recourse.
Thanks for reading my Blog – Feel free to share! – Alan