Most commercial builders of aquaria use bonded square corners in tanks even with capacities of thousands of gallons, the adhesives are not a "glue" they are a mixture of solvent and acrylic and if properly used produce a weld. Cylindrical tanks are manufactured by bending a sheet into a ring and solvent/acrylic welding the joint, this is subsequently sanded and polished to a near invisible join.
I wouldn't buy a tank with a bent corner in it unless I'd specified that in my order, I'd go to a manufacturer capable of working with industry standard materials to industry standards.