lower case part question

I'm thinking about purchasing a 2007 macbook pro a1211. its kinda beat up and will need the lower case replaced. rather than search ebay, i think ill purchase the part from ifixit. i found the part, but what I'm concerned is the quality of it. the page for the part lists it a "used, tested and grade a". what does the grade a mean and where does the part come from if it is used? will it be the whole thing i needed just like i where to have purchased it from apple? thanks all.