Slight retouching to plain grey background, four (possibly five) hi-res images

I have a number of high-resolution (22 Megapixel) images shot on Canon 70D, where the vinyl backdrop background is not quite even. Vinyl backdrops tend to sag very slightly. The job simply requires the removal of the slight variations of the background, but I do want these images to remain in colour and there should be no changes to the overall brightness or contrast values as these are part of a larger set of images. I attach PART OF one sample image just so you can see the slight problem. Do not work on this sample as it forms part of a larger image. I definitely need four images worked please. I'm looking closely at a fifth and haven't yet decided if that fifth one needs to be edited or not. I need the images returned at their original size as JPGs please by 0700 GMT 27 April so I will make a very quick decision on who to employ. I can supply the original RAW images if required but they are a little bit darker. The complete set of full size images will only be supplied to the winning bidder. IMPORTANT NOTE =============== I will check feedback on previous work you have undertaken. If I see any instances of you working on activities that are illegal in the UK within previous work you have done, you will be wasting your bid. These include, but are not limited to, removal of copyright marks, altering official documents, etc. Such work is criminal fraud or forgery in the UK and many other countries and I will not employ anyone who has undertaken such work. Finally please, to show you have read this requirement, please start your proposal, "I have read the important note." Thank you.