While I've never sold it myself, the markets around here have them in closed plastic bags in iced coolers with signs above them posting what's available & the prices.

Summer temps here are between 90 & 100, & regardless of bagging/misting, greens would wilt in an extremely short time.

Lettuce lasts a lot longer in a closed plastic bag than an open plastic bag, misted.

I sell all my leafy greens in closed plastic bags. I generally put no more than 3 bags out at a time and leave the rest in a cooler with icepacks and replace the bags as they sell.

the big lettuce guy at one of my markets sells his out of coolers that he fills with ice and has in shade. This works for him, though he has to throw out anything that does not sell.

I find that during most of spring, I can just wait till around sunset, sprinkle the lettuce with a hose before picking to remove field heat, then open bag the heads and leave them in large bins with the bags open. I bag 3 types(romaine, green leaf, and red leaf) in each bag. I've found the red leaf provides an immediate attraction for customers, I roll the bag edges down to display the colors and keep 4-5 bags visible.

It helps a lot to have a helper hold bags for me sideways while I cut, trim, and insert the heads so that each of 3 types are visible to the customer.

During the night, so long as temps get down to 50-60, the lettuce gets chilled naturally, and by morning I can then transfer about 1/2 the bags to an unchilled cooler and get by till noon.

The first bags to be sold just get kept in the bins covered with a cloth, sometimes moistened, which provides some evapo-cooling. The ones in an insulated cooler I save for later sales during the morning. I haven't had to use ice yet.

Once nightime temps get up to 70, I find it's too hot to grow lettuce anyways.