This is a custom offer. When a buyer wants to place an order for a lower or higher price than your package, he should send an offer according to his price
You broke the Fiverr rule this is clearly stated. Now if you think you haven't broken any rules. If you are sure. Then you contact fiber support and inform them about it
First of all, if the order is canceled it will affect your gig. But because of this, your account is also affected. For that, if the order is canceled, the rank of the account will be down. Not just one gig
You can further revise Buyer's work by observing it better and you can request the buyer to withdraw the report. If the buyer is a scammer, please contact Fiverr Support with your proof.
There are many pages on social media, where people find sellers for work. You get added to those pages on LinkedIn FB to get work from them. This will be the best marketing for you
If your buyer is not satisfied with the work, he can cancel the order through Fiverr support. In this case, you would be better off talking to the Buyer. After that you can contact support