Car Wrap Artboard Size?

Ensuring you  have  Window > Control  ticked

Select   just a photo and  in the bar at the top what is the PPI: showing ?

If the design consists of VECTOREL objects, magnification will not be a problem.
You can upgrade to any size you want.

PIXEL in the design, you can not work in any size if you want the photo.

You should check the resolution of the pixel images. Your designer should send you an open document instead of PDF. If you wish to open the photos in this open design document PHOTOSHOP you can perform the necessary enlargements.

sscrush,

You can work at a scale, any scale, if you just ensure that the Effect>Document Raster Effects Settings are set sufficiently high to get the right resolution at the final size (if you work at 1:10 or 1:12, you need to set them to 10 or 12 times the required final resolution or similar).

The resolution of a photo at the final size is determined by the pixel x pixel size and the final actual size. When you place the photo in an AI document, there is no resampling so if you scale down the size the resolution will increase correspondingly; there is no processing of the photo at all.

So if there is an issue with the photos is has nothing to do with AI: it has everything to do with the (original) photo.

You can choose a suitable scale that makes it easy to create the artwork.

if it is a vector image in the AI file, it can zoom in and out as much as you want with no weirdness to resolution. You should contact the print shop and ask them what file types they want. They may be able to convert right from the pdf.