Advice

The easiest way to avoid this is by not perming people you don't know! That said, you can remove lava pretty easily by standing in it and typing //drain 100. Please be more careful with who you perm next time

 

/save is bugged and we don't know how to fix it - we didn't disable it on purpose

 

That "extremely lovely staff" didn't disable /save on purpose. It wasn't working and there was no choice in the matter. I know you're upset, but keep in mind that /save never used to be an option at all. There will be bugs. They ask that you please remain patient with them as they work on it. No one will leave you hanging. I promise.

 

What pressure? All you have to do is type two characters to someone you don't know.

 

You want to be less rude in denying a stranger from building on your world? Just say "Sorry I don't know you."

 

Kind of late input, but here's some alternate advice when you're looking for friends:
Screen people who want to join.
Ask them, "can I see your map?"
Go to their map, confirm that they are the builder with /perm, and see if it's actually any good.

If it's a big group map, deny. Tell them you need to see solo builds first.

If it's a small house or something that didn't take much effort, deny. Tell them that you need to see a bigger/more detailed build before adding them.

Many griefers haven't even made their first map. People who invest time on their own maps know the effort it takes to build and usually won't ruin it for others.

(an alternate option, but adding is always still at your own risk. I had about 50 people added on Derpland at one point, and only one minor incident when I got lazy with screening.)

 

There is another issue with griefers though. Most griefers use "//set" in order to grief, which can not be avoided or fixed with "//drain".

My opinions and ways on avoiding grief are:

• Track players you want to perm. Make sure they are not griefers by simply going to their maps and confirming it.
• Personally, I duplicate my builds on a another map (yes, I have 8), in which I give no permission to strangers.
• Make sure to keep them as visitors for some time, so that you get a better opinion of the player. I learnt this trick from an old player @OliveAl; he kept me as a visitor in order to understand me better.
• Until a new permission is launched, you ought to permit anyone for as long as you are online. Before you leave provoke everyone to visitor but inform them of that.
• Have a long trusted player be the manager for your world, regularly checking the world and the players.
• And the simplest rule of all; make your world private if you have enough amount of players in your world in order to avoid more players asking for permission.