Man, having worked in a couple research labs in a previous life, there's no way I'd use a used lab scale for food. Especially when $50 will actually get you a pretty decent scale that has not been potentially used for weighing everything from diseased mice to stool samples to unidentified precipitates from a failed chemical reaction.
Since you're here to type this, it was probably not used for anything too nasty, but I do not endorse that as a way to save a few bucks!