Rebar is usually ordered as a diameter and a grade, and the grade is what the structural calculation depends on. HRB400 and HRB500 describe a defined yield strength in the Chinese series, while ASTM A615 Grade 40 and Grade 60 describe the equivalent in the American series. They are not interchangeable without a check.
The second decision is the standard the bar is certified to, because that is what the test result is measured against. A quotation that names only a diameter tells you nothing about either. Ask for the grade and the standard together, in writing.
Finally confirm the length and how it is toleranced. A bar cut outside the length tolerance cannot be bent or placed as the drawing assumes, and rebending it on site costs more than ordering it right. Send us the grade, standard, diameter and length and we confirm what we can supply against them.