The basil plant is showing signs of switching from leaf production to flower and seed. It looks like a fairly mature specimen that has been pinched back a number of times to harvest tips and leaves, but it all looks pretty normal - the leaves curling under is also normal in a large plant which has probably filled the pot with roots and can't quite keep up with the water supply to the leaves because there is no spare room in the pot to keep extra moisture. Basil leaves are quite soft and lose water easily particularly in full sun.
From this point you could shock the plant by pinching it back really hard, knocking off some of the root ball and repotting in fresh soil so that it can go back to producing more vegetative growth. This would cause the new leaves to flatten out since they would have access to more surplus water in the soil.
Generally speaking when looking for plants it is wise to choose a young one which has yet to fill much of the pot. It might be tempting to select a more mature specimen but they are that much closer to the end of their useful production period.