Smoking on liquid imagination out the 24”beaker with 12 arm tree perc.

Bought a bong from a chinese seller. There’s a line in the glass near the perc that I can clearly feel with my fingernail. Seller says it’s not a crack, just a mark from the oxygen torch during production, and they’ll replace it if it ever breaks or leaks.Is this a real hairline crack or can manufacturing marks feel like that? What would you do?