One of the key things to be very careful of are claims that chip companies make as only the reputable ones can back up their claims with a dyno. Even then, you have to be careful as they might claim a specific peak increase of xx hp, but the reality is that it was at a specific rpm and actual peak hp hardly increased. Some of the false claims I ran into while browsing the internet for performance chips for the 2014+ Corolla are ones that advertise gains of 35hp which just will NOT happen on a 1.8 litre with a simple chip, fuel economy increase of 5mpg, crisper shift points(hello, this is a CVT!), and so on.
The other thing to keep in mind is that you will also be playing with fire when it comes to your warranty. While the law states that they have to prove a modification caused a part to fail, the reality is that the burden is on YOU to prove that your mod did not cause the failure. If you want to get a lawyer and try to fight it, good luck.