Thanks All. The various suggestions are all good. I probably misunderstood the Alamy market which is predominantly publication. I come from the school of scan once - purpose many, so bigger original is better. My training is technical, not marketing so I tend to be precise rather than subjective. Member support has confirmed that QC only looks at 100% without taking into account scale factor. The suggestion to downsize anything questionable is a neat way around that. Regarding MDM's comment about Coolscan 4000, that by definition is 35mm which is one fourth the image size of my 4x5. However, if you have a really great image that you want to salvage, try selecting the sky (where grain is most prominent) and give it a little blur.
I am new to Alamy and sent the requsit 4 submissions for initial QC. They are all Tango drum scans of 4x5 (5x4) film which have been used for fine art prints as large as 40x50 inch. Nobody ever complained about sharpness. All files are 200+ MB Tiff before JPEG conversion. They are 9000x7200 pixels which is about 8 times the output from a DSLR. All were rejected as "Soft or lacking definition". When scaled down to 3600x2880 pixel which is about a 30 MB file they are tack sharp. If QC looks at everything with 100% zoom it is like looking at a transparency with a 30x microscope instead of a 4x loupe. Under those conditions everything looks grainy and fuzzy. Has anybody had the same experience? Is it a matter of giving too much information? If so, changing my workflow to down-res everything to 3600 pixel max. dimension should hopefully fix the problem. Thanks, Tom