I've included a human character that the party sees in passing

Find out what the players think he is and use your favorite explanation.

>>51812048
Have him gather a LOT of camels.

>>51812048
Identical octuplets

>>51812048
Is doing the same occupation in every town, such as medical practitioner or police officer.

>>51812048
Merchant who knows adventurers are usually flush with cash and is just waiting for them to need something he has.

"MY CABBAGES!"

File: MarcusBL2.jpg (316KB, 1920x1080px) Image search: [Google]

316KB, 1920x1080px

>>51814599
>GUNS, GUNS, GUNS GUNS GUNS!!
or if more setting appropriate
>SWORDS, SWORDS, SWORDS SWORDS SWORDS!!

He's tailing them because he's working for some faction or another and "opportunist merchant following adventurers" is just an in-plain-sight cover

File: NurseJoy.jpg (36KB, 600x450px) Image search: [Google]

36KB, 600x450px

I once had identical barmaids that showed up in every tavern across multiple cities that turned out to be the same disguised succubus teleporting around.

>>51812204
>dating different monsters

File: Demonic+scum+_fb3cda9bd403232b3d5edef209c17ac6.jpg (282KB, 1066x918px) Image search: [Google]

282KB, 1066x918px

>>51814716
I could totally see a paladin falling for that one

>>51812048
Giant underground plant monster with vines that look like people which emerge in a number of different cities.

File: hqdefaultCAIVS0T8.jpg (14KB, 480x360px) Image search: [Google]

14KB, 480x360px

>>51814686
>That merchant
>Not THIS merchant
Shame.