If you still have the fish.....
Use a 1 quart gatorade bottle. Peel the label off and scrub the glue off with hot water and an abrasive kitchen pad.
Put his food in the bottle.
If the fish happens to see you coming, and swims back out, you can simply leave the bottle in the tank for a week or more. Don't put his food ANYWHERE but inside that bottle. Trust me, he will not starve. He may not go near it for a few days, but hunger will win out in the end. Let him get comfy with the idea of swimming into that bottle to eat. Give him a few days of happily swimming in and out of the bottle at meal time. He'll get used to it and won't be expecting it when you slam the net down over the top, a few days or weeks later.
You could literally train the fish to swim in the bottle at meal time or anytime you want to capture it. Get it used to swimming in the bottle to eat. When your buyer shows up to take the fish off your hands - you simply put food in the bottle and sit back while he greedily swims into the bottle for a mid afternoon meal. You'll have him trapped in a portable vessel in less than 2 minutes.
One captured wrasse.
Ya just gotta train him first. :beer: