Pets at home keep them for ages with no regard to their requirements, and don't seem to replace until they've been sold. Trouble is, they are in the blisters deteriorating all that time. And even if they look good, they can be on the point of collapse, usually when you get them home. Best to find out when their delivery is due and pick up what you want within hours of then going on the shelves
There is a George farmer video on his youtube channel that shows how tropica grow their plants. I would guess these blister packs are the ones he shows growing in the tents that are in their greenhouses. If that's the case I don't think there would be many aquatics pests to worry about.
Yes all the European growers grow plants out of water.
They are then posted to specialist suppliers who keep them out of water also, most pet shops will bung them in their tank full of water.
Some pet shops will request the same plants packaged in the blister packs. It saves them either having a specialist out of water holding facility or a tank full of water.
you can never totally avoid snails. Yes you can use tissue culture plants, these are the only plants that will never have snails or pests.
However snails are like ninjas and will just appear out of nowhere In your tank at home!
Best bet is to buy them from a specialist supplier that has a high turnover and plants are not put underwater or avoid buying plants from tanks at the lfs that look like they have lots of snails in them. At home you will only really have an issue if you have too much waste/stuff for the snails to eat.
To get the best plants You want to buy plants as fresh as poss. So either from a specialist place that has a very quick turnover or get down to your lfs on the day they arrive.