Can I give my twitter username to my buyer.Is it violate Fiverr rules …
Hm, I think it all depends on the context of your message!
If you say something like - contact me using this e-mail/phone/twitter/facebook/skype - it is definitely a violation of rules.
But if you need to provide your contacts for the job to be done it is different. Like I ordered a visit card design, and I ask seller to put there my website and an office phone number. How else can he complete the work, if I don’t have any designing software installed and simply unable to change any text on my own? If you order, let’s say some facebook likes, how can you do that without sharing that facebook contact? How can someone make a video testimonial to your site without having a link to it?
Just make sure you don’t (or intend to) contact anyone outside the fiverr! And please report to Customer Support if someone does that to you using any of provided contacts.
And yes, better ask support if you are not sure about rules.
I’m guessing as Facebook is not permitted in messages then Twitter would follow the same rule.
Mike has some great advice for you there !