Nonsense if your SA say might void warranty.
Eco tint does not cost so much, and the SA is only after his commission.
Go do your tinted outside, 3M is a much better tinted film and better performance., try crystalline

Don’t believe any voucher from SA, it is actually used for them to get commission from the shop, I once checked you can get cheaper price outside without the vouchers, and trust me, no such thing as you do tinted outside, will void warranty, they use this tactic to scare you only.