How To Close Paint Cans
There are multiple ways of closing paint cans but some are better than others. Just putting the lid on and stomping on it will not give it a good enough seal. Whaling away at it with a hammer might damage the lid and have the same effect. The best way to close a paint can is to first clean off any excess paint from the rim. If there is old dry paint on it, try to scrap off as much as possible without jabbing the metal. Then, put the lid in place and use a large mallet to gently tap it back on. If you do not have access to a mallet, you can place a thick rag over top and gently tap the lid closed with a hammer. Go around multiple times to ensure the lid is sealed all the way around.
How To Transport Paint Cans
If you are picking up new paint or moving used paint cans from one location to another, make sure they are closed properly, especially if you didn't personally close them. Secondly, ensure they are upright and secured. Place them in a cardboard box, tie them with bungees or barricade them with other items so they can't move around. If you have no other option and they have to be placed loose in the back of a truck, note that the cans can flex and open on their own if they are tossed around. In that case, it's not a bad idea to add some sort of tough tape to secure the lids.
Now excuse me while I go clean this mess. Which important step do you think was missed here?