Over the many years of painting driveways, garage floors and pool decks I have learned many things. In this picture you see a concrete pool deck with a crack. If you look close enough you will see where it has been patched in the past, and the crack has come back. When I am meeting with homeowners to give them estimates on painting their pool decks I let them know what we do not fix the cracks. Concrete will expand and contract, then crack. Once cracked, the crack always comes back. I have tried many different materials to seal in the crack so it never comes back, and I have not found anything that works. If a homeowners wants to hide the crack I recommend installing brick pavers over their pool deck.
However if the cracks do not bother you, we will be happy to paint the deck, however their is a science to painting decks.
Not all paints or stains that are used on pool decks, driveways or garage floors are compatible with other paints or stains. If there is a Xylene based stain that was last used on the surface you have to go back with Xylene, you can't put a latex or acrylic product over the Xylene, and Visa a verse, you can't put a Xylene based product over a latex or acrylic product.
The best procedures I have found when painting over a previous painted or stained surface and to ensure adhesion is to pressure clean the surface, allow to dry then put down a oil based bonding primer with a 24 hours dry time, then put down an acrylic stain on the concrete surface.
If the surface does not have a coating on it, then be sure to pressure clean the surface, then acid wash the concrete with Muriatic acid, pressure clean again and allow to thoroughly dry for 1 to 4 days. Then apply your stain, either xylene based or acrylic stain. I always like to add an anti-skid to the stain to make sure the finished surface is not slippery.
The pictures of these pool decks, we followed these procedures and we never have a problem with adhesion.