online seed sales are pretty safe, but do research first. I look for popular seed banks. buying them offline? like from some guy on the street or from a disp.? I would never buy seeds on the street, almost a guarantee you will not get what you are paying for. Our disp. do not sell seeds only clones, so I have no knowledge of seeds from disp.
The single seed centre, and Attitude seedbank both ship discreetly to the US. I've had several good experiences w/ the first one, the second one gets alot of good reviews. Don't worry about it. You'll be just fine.