I was wondering 
,
Is this allowed to ask for a tip from the buyer? My client wanted a job and he was not sure before asking what he needed. After taking the order, I could understand the job was may more than he wanted. In this way I had to cancel an order which affected my stats for a while.
But what if I know how to do the job and ask for some tips to my client, so that the loss of the work is diminishes by the effect of 
$$ really.
Is this ok on fiverr?
Please help
Asking for a tip may or may not be against the rules, but I’d consider it bad form. If I were a buyer and someone asked me for a tip, I wouldn’t want to work with them again.
You might consider highlighting the work that you already did, bringing up the ways you exceeded expectations. An impressed client may tip you on their own, but don’t make it seem like you’re fishing for compliments.
Nice suggestion 
Thank you
You can add an extra to the order
You just take more order for that client and convince him that you have enough time for that order and them take another order from him thats the simple way i think