It is almost understood that Freelancer's mostly don't have polished work who never got chance to do job under someone's supervision.
Sorry. It's not "understood". In fact, I find it quite rude if someone approaches me for work assuming I don't know what I'm doing.
If anything, the "understanding" would be that a freelancer has enough practical, real-world, experience to complete their work in a polished and professional manner.
What you are describing is a hobbyist, not a freelancer.
If you don't have any real-world experience, you need to get some. Daniel points out a few ways in his answer as well.
- Get a real job in the field you want to freelance in.
- Hire an experience professional in your field to review your work, and be prepared to redo it.
- Get a formal education
- Worst case, disclose to potential clients that you have no practical, real-world experience.
If you can't do any of the above, then in my opinion, you should not be "freelancing".
Truth of the matter is you should not be asking others to pay you if you have no practical experience, and aren't disclosing that fact up front. Doing so only serves to devalue the entire field you are attempting to work in. In short, you give everyone a bad name if you don't know what you are doing.