In discussions about the importance of monitor calibration, it’s common to see this argument:

“My clients don’t have calibrated screens. If I calibrate mine, my photos won’t look the same to them.”

This is absurd for two reasons.  Firstly, uncalibrated screens are like human beings – no two look the same, anywhere, ever.  So to suggest that leaving one screen uncalibrated will ensure it matches another uncalibrated screen is complete nonsense.

Secondly, consider this …

We just had our bathroom renovated. We chose a good builder, and paid him top dollar, and he did an excellent job. He built us a perfect bathroom.

Trouble is, I’m a lazy housekeeper, and I tend to let it get a bit grubby, you know? I don’t clean it as often or as thoroughly as I should. If you were to visit right now, the bathroom wouldn’t look as good as it did the day the builder finished.

So, does that mean it would have been ok if the builder had done a shabby job? Hell no. We paid him for a perfect bathroom, and that’s what we got.

Should your clients be happy to pay you for less than perfect photos? Of course not. Your job is to “build a perfect bathroom”, so to speak. To provide wonderful photos, and monitor calibration is a vital part of that.

If your client then views your photos on their awful screen, or hangs them in a room with awful light, so they look less than their best, is that on you? Of course not. 
What your clients do is irrelevant. The onus is on you, the professional, to be correct.