As far as the contact info issue, it’s usually not an issue if a buyer sends it to you occasionally without a prompt and you just tell them it’s against the Fiverr ToS to contact outside. If you are getting a lot of buyers sending it, that’s unusual, so be careful you aren’t somehow giving them the idea that they should. Make sure you don’t use any “red flag” words yourself when you message, even if it’s an accident. Another thing you can do is to contact CS immediately if a buyer gives you contact info. Just let CS know you didn’t ask for it and you want them to be aware of that. Don’t make too big a deal of it, just state the basics.
As far as the $5 issue, it sounds like between that and the contact info thing, you may just be having trouble with communication. If someone orders a website for $5, you already have a package set up for them offering a 2 page site. If they ask for more, all you have to do is cut and paste from your own gig offering what you do for $5 and Customer Support will back you. If the buyer wants more, point out exactly which extras and which packages they need for that. If you stick to your own gig description, speak politely and be a professional, a buyer can report you if they want to but that won’t do them any good.