re: "I need advice regarding the refund policy. If any of my client ended the contract after receiving the work from my side, so still he eligible to refund his payment from me?"
That's an interesting question.
The basic "policy" on Upwork - and this is same "policy" dates back thousands of years when it comes to work - is this: When you hire a person to work for you, you pay them money. And they keep the money.
On Upwork, there are "refund" mechanisms.
https://support.upwork.com/hc/en-us/articles/211062088-Request-a-Refund
https://support.upwork.com/hc/en-us/articles/211062058-Get-an-Escrow-Refund
But these are really meant to be used by FREELANCERS if it turns out that they are not going to be able to do the work for some reason.
The time for a client to deal with an issue, and ask for a refund, is really BEFORE the contract closes.
AFTER a contract is closed, it is possible for a client to ASK for a refund, but the client has lost most of his leverage, because he has already left feedback.
The MAIN WAY THAT REFUNDS ARE HANDLED after a contract has been closed is that a client can ASK a freelancer for a refund, but the freelancer can say no.
Aside from that, Upwork may offer some limited "refund assistance" to a fixed-price client for a period of 30 days after paying money to a freelancer. This is essentially mediation, trying to facilitate communication in asking the freelancer for money.
My advice to freelancers:
If you work for a client and then the client asks for the money he paid you, the client is being unprofessional, immoral and unethical. Don't give a client their money back if you actually did the work.
My advice to clients:
You will save time and money if you proactively plan to never ask freelancers for money. No matter what. So if you pay a freelancer, just plan on that money being gone forever. This will help you manage your freelancers and contracts in a more effective way. Instead fo paying money to an underperforming freelancer and asking for that money back - which is a gamble - it is better to do this: Monitor a freelancer's work, and if you don't love it, then fire the freelancer. If you STOP paying money to an underperforming freelancer you are much safer than if you pay that freelancer money and think that somehow you can get that money back later on.
