Exactly as pacef8 says, unless specified, most printers will reproduce the supplied image as is. When I worked in print, doing prepress, I would generally try to improve any illustration as quickly as possible, but if supplied with an illustration that seems to be as compromised as the OP says, then we would ask for the original a/w, or a much better quality photo. A photo that changes colour from top to bottom, no matter the resolution, is going to take a lot of phaffing around with, involving things like layers, graduated fills, etc, to try to balance the colour differential, which may involve an extra hour, maybe two, to get a decent result, which could add an extra £100-150 to the cost.
As the customer, the OP should have been given a colour proof, matched as closely as possible to the final job; it’s at that point that any issues that come to light should be pointed out and, if possible, corrected.