halacha - Working in a non kosher yogurt store

I was asked a question this afternoon and I don't know a good answer (yet) so I'm posting it.

I have been asked in the past whether a Jewish person may work in a non-Kosher restaurant that serves meat. The answer I have heard and read is that one may not and one reason is because you may not serve a Jewish customer a treif meal. (this is a gloss but I can't find the source sheets for the shiur about it).

But what about a yogurt place which has no hashgocha and the patrons effectively serve themselves. Sure, the store has gummy this and marshmallow that and I know that they are of a treif brand, but I am not serving anything. Is this more like being a cashier in Shoprite where I don't control what people put in their baskets, I just collect money? Or is this still a restaurant and I can't facilitate someone's choice to eat non Kosher food?

I know this overlaps with this question but it isn't exact because the person is eating right then and there. And if I find my source sheet, I will try to give the basis for my assumption that one should not work in a treif restaurant.

And yes, I intend to ask the LOR when I see him but I'd like to amass as much info as I can beforehand.

---

Edit -- the LOR didn't come in today with any sources but I looked in The laws of Kashrus (Forst) and on page 182, under the heading of "beneficial use" it reads (unless someone can find the text online, my copy job will have to do - I moved footnotes to parentheticals and omitted unnecessary commentary)

"One may not engage in any commerce involving basar b'chalav. One who owns a restaurant with a non-Jewish clientele, may not serve basar b'chalav. Incidentally, one may not engage in commerce involving any foodstuffs Biblically forbidden to eat (...see Y.D. 117...) lest one inadvertently come to eat some of the prohibited food himself. (Shach §2 and Taz §1 citing Rashba) In addition, it may be problematic selling any forbidden food to the public since non-observant Jews may also purchase food. (See Darcei Tshuva 117:65)"

---

Working in a restaurant which serves gummy bears which are treif seems to fall under the second clause (the "incidentally") even if the place is self serve, as the food is out and available and workers often eat the food in their own restaurants. Yes, I see that the broad application of the third clause ("In addition") is VERY broad but I'm simply pointing out that there is a background logic to this question. And I happen to be unable to read the tiny D"T letters so if someone can transcribe it without going blind, feel free.