What about hinge on Dell G3 15 3500 ?

Warranties vary by country of origin for a notebook, plus many countries have consumer protection agencies that require better coverage. On a new model all you can do is wait for early buyers to report on their experiences with quality. Hinges are wearable parts that can vary in quality and durability and if you don't open and close your notebook all the time even a weak hinge design might not give you problems. Check with your local warranty coverage where you plan on purchasing to read specifics on hinge coverage and consider buying extended or optional warranties that many times cover additional wear and tear. 

Wait until Dell 3590 is used by many laptop users.

And let them pass their judgements about the product's hinges.

Once all of that is done then you can decide whether to buy the laptop or not.

G5 SE 2020 has similar chassis too. I cant wait for 7 months. If one machine starts making headache on me even without buying it then I should stay away from it.

I am currently using a Dell G3 3590 model purchased in May 2020. We started seeing some problem with the hinge 1 month into the usage. When the laptop lid is opened the hinge moves slightly to the left and this is seen once we close the lid. It doesn't align properly with the base of the laptop.

Initially we thought its a minor issue and we could get along with it. 1-2 weeks later the hinge started to break and now it reached a stage where the front panel is sticking out as it'd come out of the base anytime.

We managed to initiate a complaint with Dell customer service folks and they agreed to replace the device with a new one, its been 1 month now we are yet to receive the laptop. We tried requesting for a completely different model but Dell folks said that's not possible. So we are stuck with this one, afraid even after getting a new device we have to use to with extreme care.

I strongly recommend against buying this version, the hinge is very weak and could lead to issues at some point of the device lifetime. Material is also not sturdy, to be honest feels cheap compared to similarly priced non-gaming Dell laptops made with plastic outer casing.

I can tell you that as of today, the G3 15 3500 has hinge issues, purchased October 2020.

6- If hinge gets broken on 3500 can i get free repair? In which countries?

Not in the US. I just spoke with technical services. 
7- If hinge gets broken on 3500 can i get free repair after warranty is over?

Not at all in the US, even within the warranty. It is outside the scope of the warranty and considered "damage" even if there is no damage.

i bought Dell g315 3500 in nov 2020, and I found it's hinge broke in Dec 2021. In almost one year it broke. And they said it's not design issue because they have not received such complaints. But I can see there are lot of complaints all over the internet. What scam they are running

I am a bit late on this reply. I had bought a 15 3500 series laptop in Oct 21 and yesterday (Jul 22) the right hinge broke. This laptop is used like a desktop and is hardly taken out of table. The laptop is closed on a average once a day in the evening when I wind up
Checking on forums it seems to be clearly a design issue. Luckily here in India this seems to be covered under warranty for once in a life time replacement even though I have an extended warranty till Oct 24

The other good thing is that here in India there are 3rd party vendors who fix fix it for 10-20 USD equivalent.

What is horrifying is that the DELL service said they will take 1- 2 weeks to repair this

As has been mentioned, one needs to open and close screen from the center and not one side of screen. This is normally the right side if one is right handed