One of his regular customers is Brian Westhouse (known in Marcuria as The Rolling Man), who April desperately needs to find to get back to Stark. After he fires Ulen, his delivery boy, in April's presence, she seizes the opportunity to get a job delivering maps, hoping a delivery to Westhouse will come along. After weighing his options, Karek's greed gets the better of him (by hiring April, he won't have to pay the hiring fee to the Guild of Merchants), and he gives April the job and the delivery list, along with the first map.
As soon as April returns from delivering her final map to Tun Luiec at the Journeyman Inn, she goes back to the Maps stall where Karek promptly fires her, saying "You're the most incompetent delivery boy I've ever had!" It's the last time that we see him in The Longest Journey, as his stall is empty right before the Tyren invade Marcuria.
You can ask him about Stark before you learn about it.