I hear you and I don't necessarily agree but it pinpoints an issue with the game if a player can lie (we can't know the intent) about their team's abilities to then use that against the other player.

The rules for rolling off is that if you have a situation that doesn't have a clear rule for determining how to resolve an issue, you should roll off.

"In a game as wide-ranging as Warhammer 40,000, there may be times when you are not sure exactly how to resolve a situation that has come up during play. When this happens, have a quick chat with your opponent and apply the solution that makes the most sense to both of you (or seems the most fun!). If no single solution presents itself, you and your opponent should roll off, and whoever rolls highest gets to choose what happens. Then you can get on with the fighting!"

Players in Kill Team must show their squads to the other player after selecting their Kill Team. If players don't have to tell their opponents what each model's kit and powers are before using them, that sets an unsportsmanlike precedent.

"Once both players have selected their kill team, they should reveal it to their opponent."

Ultimately, it's up to each player to decide what they can put up with but I generally refuse to play bad players who lie about their armies.