Yes a scammer can change their IP address and a few other things to remain undetected, but this is why we have multiple levels of verification. Getting a new Paypal account and phone number is very time consuming and if the scammer is constantly getting banned and remaking accounts, they are obviously aren't going to try to get verified each time because they know they will get caught even faster.
For $3 there really isn't any good reason why everyone can't get verified especially if your buying or selling accounts regularly.
If you're dealing with a new member and they don't want to get verified just tell them you'll pay the $3 verification fee by either adding it to the cost of your purchase or subtracting it from the sale. If the person still says no, they are 99.999999999% a scammer. Very easy way to weed out scammers this way.