KeeleyWray there is the possibility to make jewellery stores if you have either Get to Work or Business and Hobbies to make the store. You then need Crystal Creations to make the jewellery to sell. It works better with GTW retail lots for me as I use larger tables to display them all and then set them for sale individually. The B&H method alone of displaying items for sale doesn't allow for enough tiny slots to display the rings and smaller items of jewellery for me. I use dining tables to put them out on display as I find that lets me sell more items. I often have a Sim in mind when I create jewellery collections like gold with amber or silver with moonstone. My new Sims will head over to my jewellery shop and buy the collection my jeweller Sim made for them. Sims can also propose with a ring they bought but each ring is already pre assigned to a specific finger so they can't wear it on their wedding finger.
For your socially anxious Sim idea, you could try the Loner trait if you haven't already. It makes Sims very nervous around crowds and in public places. I tried it on a federal agent Sim who I wanted to be a lone wolf fed but unfortunately it just made her too anxious around people. Its more socially anxious rather than Loner. She became really stressed just going into any public place.