trying to figure out what's wrong with these shrimp

ETA: He's selling them thawed. So, now how can I cook them without them turning into mealey mush?

bought shrimp from a shrimper (he came to the house). The shrimp don't have heads, are fresh looking, don't smell, but turn to total mush and are mealy when they're boiled. They are not over cooked.

Haven't fried them, so don't know who they'd do then.

Trying to figure out what's wrong with them. Could he be thawing them before selling? Bought a lot, so we froze them.