depends. Very slight puddling during/right after a rain, that quickly goes away, may be ok in some circumstances. Anything that stays for a significant amount of time, though, or is holding a good bit of water - problem. Can you post photos, both dry and holding water?

@germainetoo I hear your frustration. Obviously this is based on some internet pics and some guessing/inferring, but here are my thoughts as this discussion has progressed: I'm coming back to "it's wet quite a bit" under the deck, and also "it constantly is wet". Is the sole source of your water woes what's coming through the deck, or is this a low area? are the gaps between your deck boards crazy wide or something? What was under the deck previously? If it was bare soil, were there visible erosion lines that matched up w/ the decking? Is the patio pitched appropriately to shed water? how much time elapsed between poly sand installation and first rainfall? If rain is coming within the first 24-72 hours the patio will need covered to another poster's point, if an under-deck ceiling were a requirement for a below deck patio, we'd see about a quarter as many as we do. We generally do them as a way to 1) keep the area totally dry and 2) make it not feel like you're... under a deck. It's hard to say if a ceiling could work in your situation without seeing the whole area, as we generally pitch away from the house and towards the deck beam. That gets collected in a gutter mounted to the beam, and that water exits via a downspout run down a post and ideally piped as far away as possible. Bottom line, there may be an oversight or there may be other factors at play here that weren't discussed or brought into the scope of work.

You could have problems in two potential spots. 1. as we have discussed, the water has to drain away from the house and away from the patio. 2. the water has to go somewhere and it could cause erosion in that spot, or puddle up. In that case, you can "drain" it away, but again, it has to have someplace to go. Or, it can sink into the ground at the "away" spot, so as not to cause a problem. Most yards have a combination of the two strategies. This is usually calculated and worked out before hardscaping, since hardscaping ipso facto causes a drainage concern since the hard space is no longer absorbing water. One can determine how much water will run off by calculating the area of the hardscape plus the annual rainfall in the area. Plan for the larger end of the possible rainfall spectrum.

they failed to grade correctly. It was poorly done. I'd call them back out and have them fix it. (and it's going to have be taken up and redone, regardless. no way to fix that slope without removing those (or, I suppose you could put in a french drain near the foundation. But why should you do that when the patio is supposed to be graded away from the house?? doesn't seem right) BTW, were theses pavers set solely on the dirt/sand? (also the cheap way) They should have poured concrete first, and then laid the pavers. within a few years those pavers are going to shift/sag and move. Ask me how I know.