As others have said, the blade quality and condition will have a large influence on the saws ability to be adjusted for a straight cut. If a good blade, prperly tightened with properly adjusted blade guide rollers still fails to cut straight, then the easiest alternative is to shim the guides as Conrad_Turbo did to for the blade to be perpendicular to the work.
You should also check the travel of the arm with respect to the plane of the vice. Place one end of carpenter square on the vice with other vertical end near the blade. Now, raise / lower the arm and watch to see if the blade remains the same distance to the square. If not, then the pivot is not square to the base and the vice surface. Shimming the guides can compensate but for a major misalignment ( and returning the saw is not an option ) the other option is to drill one of the pivot "ears" that the pivot bolt goes through and making an offset bushing to correct the alignment. That's what I did for my saw. It was off by at least an 1/8" over a 4" rise. It now cuts straight.
Here's an old pic, when the saw was new, with the stand I made. A sturdy stand will also guarantee that there is no misaligment due to flex in the base from the flimsey legs that these saws come with.
"Research is what I'm doing when I don't know what I'm doing"
Lincoln ProMig 175, Thermal Arc 185tsw, Hypertherm Powermax 1000
HF 4x6 bandsaw, DeWalt 4.5" grinder, Homier compact bender
JD2 model 3 tubing bender
Cummins 7x12 mini lathe, Homier mini mill
Plasmacam CNC table