CS GO cases on sites are very different in appearance from cases in the CS: GO game itself. On the one hand, the overall chance of winning or the payback of cases on the site is much higher than in the game, but really rare and valuable game skins on sites fall out quite rarely, which is primarily due to their absence on trading floors.
The likelihood of a particular skin falling out of different cases is determined by the cost of the case itself and the cost of the skins that are dropped in this case. Cases in Counter Strike rarely pay off, and just as rarely their cost equals the cost of dropped skins. Cases on thematic sites work in a slightly different way. For example: there is a case, let’s say «Dark Case». On the sites, its price is approximately $1.5. If you listen to popular advertisements about the payback of cases in the region of 70%, this does not mean that the skin for $1 will drop when you open it. Most likely, when you open 1000 cases worth $1500, you will get skins worth $1000. Of these $1000, more than half can fall in the form of some expensive weapon — such as several USP-S Kill Confirmed and a pair of knives. Conditional $500 will remain for the remaining 980 cases. And they will contain the very skins for $0.5-$1 that fall to everyone. So it’s up to you to choose which is better — to open cases on thematic sites or open cases in the game.
Remember that all sites are just entertainment. There is no need to approach this business as a way of earning money.