The Purple Pterodactyls by L. Sprague de Camp

The Purple Pterodactyls by L. Sprague de Camp (F&SF, August 1976) is another of the supernatural adventures of Willy Newbury.1 In this one he is on holiday by the sea with his wife Denise and, when they visit a nearby amusement park, Willy notices something at the rubber ring stall:

The prizes were even more original: a flock of plush-and-wire pterodactyls. They came in several models and sizes, some with long tails and some with short, some with teeth and some with long toothless beaks. The biggest were over a yard across the wings. They were made so that you could hang one from your ceiling as a mobile.
If the wind was strong, you could lock the wings in place and fly the thing as a kite. They were all dyed in shades of purple.
“Purple pterodactyls!” I cried. “Darling, I’ve got to have one of those.”  p. 144

Willy’s attempts to win one of the pterodactyls are unsuccessful, and he also isn’t able purchase one (he asks the stall’s proprietor, Mr Maniu, when he sees him at the beach the next day, but is refused). Willy’s luck changes later, however, when he buys an old ring for a quarter and, when his wife takes him to a jeweller to have it valued, discovers that the ring is ancient and the stone a real emerald. Then, when Willy is asleep that night, the djinn of the ring reveals himself to Willy and says it can perform “little favours” for him. Willy asks the djinn to help him win a purple pterodactyl.
This begins a spat that sees, after Willy subsequently wins more than one of the prizes, (a) Maniu hire his own djinn to stop Willy winning any more; (b) Willy going back to win a third pterodactyl when his own djinn tells him of this; (c) words disappearing off a speech Willy gives at a local women’s club meeting; (d) Willy winning another two pterodactyls; and then (e) Willy and Denise having their boat capsized by a freak squall that comes out of nowhere.
At this point Willy realises that he is involved in a potentially lethal vendetta, so he promises the djinn his freedom if he can get Willy out of his predicament. The story then ends (spoiler) with a shriek in the night, and Willy seeing Mr Maniu on the beach the next morning, his body covered in sand as usual . . . then Maniu’s decapitated head rolls off the mound.
When Willy sees the djinn in a dream several nights later he promptly gives him the ring and his freedom. Then he wakes up and has sex with his wife, as you do when you’ve just caused someone’s death.
This piece isn’t as slight a story as some in the series, but it does have a deus ex machina ending and is tonally a bit off: not only does the final line about sex with his wife not sit well with previous events but, if it wasn’t for Willy’s awful behaviour (who need five purple pterodactyls?), relations between the two men would not have deteriorated. I’m probably reading too much into a piece of light fantasy, but still. . . .
** (Average). 5,650 words. Story link.

1. The ISFDB page for the Willy Newbury series.