This makes me wonder, what if, even in a reputable casino, RTP version can be tweak like this, so for example, a casino can claim they are using the 96% RTP slot version of a slot, but it could actually turn out to be the lower version. Can this be a posibility?
If it is a licensed casino, it is most likely that this data can be seen on the provider's site and not in the casino itself, and as for your question about whether a licensed casino lies about it, it is possible but unlikely since they are audited and regulated and will not want to damage their own reputation because in the same way the house always has the advantage, so cheating to win more money would be like shooting yourself in the foot out of greed.