price and depends on the expert

I am assuming that by simulated diamonds you mean diamond simulants such as rhinestone or cubic zirconia and by lab-created you mean synthetic diamond.

Simulated diamonds are NOT diamond, they are not the same chemically (or mineralogically). Rhinestones are glass or acrylic and CZs are ZrO2. Diamond is all carbon. Synthetic diamonds, however, ARE the same chemically (and mineralogically) as diamond, they were just created by humans in a lab instead of my nature deep in the Earth.

Synthetic diamonds, since created in a lab where we can control conditions and impurities and such, are going to have BETTER clarity and such than natural diamonds. Since they are the same chemically as naturally occurring diamonds it is indeed hard to tell them apart because they ARE diamonds. Spectroscopy (infrared, ultraviolet, or X-ray, which uses a fancy, expensive machine) can tell the synthetic from the natural.

Lab-created or “Synthetic” diamonds are 100% real diamonds.

A diamond simulant may be artificial, natural, or in some cases a combination thereof. While their material properties depart markedly from those of diamond, simulants have certain desired characteristics—such as dispersion and hardness—which lend themselves to imitation. Trained gemologists with appropriate equipment are able to distinguish natural and synthetic diamonds from all diamond simulants, primarily by visual inspection.

The most common diamond simulants are high-leaded glass (i.e., rhinestones) and cubic zirconia (CZ), both artificial materials.

I’m no expert, but industrially manufactured diamonds are the same chemically (obviously) but are usually not as clear and don’t look as good as natural ones.

I would think an expert could tell the difference.