When the customer's photo or artwork has to print at banner size and a redraw is not the answer, we upscale it: cleaned, sharpened, artifacts removed and resized for your printer. From $5 per file.
If it is a logo, lettering or a flat graphic, a hand-drawn vector will always print cleaner and cut on a plotter. Upscaling is for the things that cannot be vectors: photographs, painted artwork, illustrated backgrounds and complex raster graphics that need to hold up at 150 dpi across a 4-by-8 banner.
Not sure which you need? Send it anyway. The account desk will tell you, and quote the cheaper option when both would work.

Clean source, modest enlargement, no retouching needed.
Typical customer-supplied art: compressed, a little soft, needs cleanup on the way up.
Heavy enlargement, damaged source, mixed text and photo, or files that need reconstruction.
Tell us what it prints on and how big. Quote first, files within 48 business hours.