It depends if you are planning to check your entire range. Two possibilities:

a) You are not planning to check your entire range regardless of flop. In this case you should obviously never check in the dark, as you are needlessly giving away information about what part of your range you have.

b) You are planning to check your entire range. In this case I hate it less but you're still giving away that you don't have a donk-bet game - you're saving villain from incorrectly discounting combos that he wrongly thinks would/might have lead out with. If you can start a fashion for it in your cardroom though you might see more hands per hour. I once suggested a new version of Holdem where action starts each round on the player with the last aggressive action - the idea being to speed up the game and also to punish calling OOP less strictly.

Partially contradicting the above, my main read is that it's someone who doesn't know what they are doing and therefore its hard to say what hand they think they would want to check regardless of flop and/or it's an intermediate player who always plays "in rhythm" and therefore is checking to the raiser all the time.

If it's scenario b) then your hand is equally unreadable if you wait to actually make the check, just your opponent doesn't know that and may adjust your range incorrectly.

It's not just that you are giving away the chance to get more information before you decide to check - it's also that you are giving information to your opponent about the fact that you didn't use that information.

Absolutely they're weak, but you already know they're weak because they didn't re-bet whatever the last raise was.

However weak is relative. Against a tight player, "weak" could be anything below 99. Against a loose player, "weak" could be anything below 9Ts.

2 main reasons people will check dark:

1. It's fun.
2. They're trying to hide information / remove some of the disadvantage of being first to act.

How about betting in the dark. I just read and update from the Rio circuit main that said a player bet in the dark as the dealer was burning a card and getting ready to lay down the river.

here

It depends if you are planning to bet your entire range. Two possibilities:

a) You are not planning to bet your entire range regardless of river. In this case you should obviously never bet in the dark, as you are needlessly giving away information about what part of your range you have.

b) You are planning to bet your entire range. In this case I hate it less but you're still giving away that you don't have a checking range - you're saving villain from incorrectly discounting combos that he wrongly thinks would/might have checked with.