I can give you a few recommendations here. First off, always print your work out (making sure that it looks good to you and matches your screen reasonably well) Send this proof to the client. Having a hard copy is the only real way you will all be on the same page in terms of color. It's super frustrating I know.
When working in RGB, use the Adobe1998 color profile. It's a very stable profile that works across most monitors. If your file isn't already using that profile, click "convert to profile under "Edit" in the photoshop menu.
If you want to change the file to CMYK (which you should if you are printing - unless otherwise directed), then use the "Convert to Profile " again and select " US WEB coated (SWOP) v2. This is a CMYK profile and will make that transformation for you. Make sure the "flatten layers" button is selected. Now save the file with a separate name so you don't lose all those layers in your RGB file.
This method was told to me by a printing guru and I've used it for years without any trouble at all. ; )