You have no choice if you buy from a reputable tire dealer/ installer. And, they are right !
Let me just add, if you were waking and turning right, notice as you step to the right with your right foot, your left foot pushes off. It’s called your “posting” foot and requires good traction or it slips first in snow.
In exactly the same way, when you turn your car, lateral force is applied to the rear wheels. If the traction is insufficient and and not nearly as good as the front wheels, you can go into a spin. It similarly occurs when braking. If you don’t have enough lateral traction on the rear when you brake, and the traction is unequal on the two front wheels so lateral turning force is applied to the rear, you will again spin out.
In some respects, it is more dangerous to have the front and rear axle with different tires then it is to have the same but less traction overall. Or, don’t put any snow tires on if you can’t put them on all four. Spinning is worse then sliding in most peoples minds and thankfully, most tire sale’s people’s requirements.
Where you are not used to driving in snow, BUY THEM.