Dear Mr., Ms.,
A scale for commercial purposes is specific and has its own requirements, as described in the legislation.
A scale for your QA lab has other purposes, as you described. Depending on your activities, you need to define a precision level. In general there is more than 1 scale in a laboratory, all depending of the weights you like to measure and of the required precision.
And yes, include them in the maintenance and calibration schedule, as the QA department needs to produce significant data. The maintenance can normally be done by the same company as the one who maintains your commercial scales.
I hope I could add some extra explanation for you to this complex topic. Above there was already a lot of valuable information. I liked to add a bit more, as you are actually buying scales.
I wish you good luck and good decisions!