Why GPS and Galileo still need a way to resolve disagreement

Does using both GPS and Galileo make commercial navigation harder to spoof?

Yes, but disagreement still needs to be resolved through another reference and checks on signal direction and quality.

Using both GPS and Galileo is acknowledged as making spoofing harder. If the two systems disagree, however, the receiver still needs a way to decide which position to trust. A third reference is suggested as a tie-breaker, alongside checks on signal direction and quality. Newer receivers are described as already incorporating such checks, which shifts attention toward older equipment. This closing follow-up qualifies the idea that adding another constellation alone settles the problem.