There are all fast fashion par quality, anon... Maybe Ralph Lauren and Calvin might have some sophisticated line of productions, but, in an overall, those are not really high quality reference.
Maybe Dior, the exclusive fashion line from Maison Margiela, Balenciaga, Versace (remember how they're aclaimmed on kamikaze girls?) or something more in this line.
The tip for finding the quality, at least for me (it surely varies from person to person), is checking the finishing first, the material second, and the construction, as a whole. There shouldn't be visible serging, no loose threads, no button spilling, no yellowing/pilling fabric, well made lining, no elastics that get loose over time, no prints that bleed, symmetric construction (when it's not something purposely asymmetrical).
Anyway, Lolita is not as expensive as High-fashion, of course, so that's probably why we can't expect these stores to have the same finishing / quality than exclusive brand pieces. My favourite brand when the talk is about finishing is, of course, JetJ. I feel like they're on the best way to make high-quality clothing, not considering those stupid moves they made on the last fashion event, of course. But they have impeccable lining, invisible hem, high quality fabric (not high quality print, though), nice fit, the construction is sturdy, there are no visible seams anywhere on the outside, no serge on the outside etc.