I got a 4.7 star from one of my repeated buyers, he was happy with the work but he after all did not gave me 5 star. 4.7 start is also a good rating, so do not worry about it sometimes it happens.
there are many ways you can pay for services on fiverr.
from the main menu, go to your Profile and under the General section, you will see Payments. Here you will see Currency, Paypal single click, and Personal balance options.
There is no way to edit the review after posting it, but about the cancel order I think you can reach out to fiverr customer support they will help you.
No there is no such system in fiverr for sending clients letters. You can improve your profile and gigs by researching then hopefully you will get clients.
I was trying to add two of my clients at my profile but it doesn't accepted properly. First one was pending and was not approved long time. Then I deleted that one and added another one again and that one was not approved where I worked both of the client's project and even the last client told me I can add them as portfolio or my profile when the project is completed.
Anyone can help me that how can I do that?
Thanks!