I've found a very minor bug, but I thought I may as well mention it.
After going to the house in question and speaking to the individual, I acted as if I didn't know what was going on. I asked to see the merchandise, closed the shop and noticed the quest updated with a check alongside delivering the ring, though I never mentioned it to them. I tried different dialogue options as a quick test and it appears that anything other than immediately taking the good bye option after starting the conversation will give that result.
