How do you do it?

I have been taking some home portraits the last couple of weekends in a makeshift home studio I set up. I have been taking all of the pictures in RAW and adjust them with DPP. Before I convert them to JPG, I have been trimming them to various sizes; 5x7, 8.5x11 and such. The photos look great when I load them to my smugmug page but, if I want to buy a print of a different size, the photo doesn't seen to fill the paper completely. I suppose that is because I have scaled the picture previously.

Does it make more sense to not trim before the conversion, and then trim the photo when I want to buy it?

have you try to tell them not to resize? Most places resize by default.

Sure, unless you definitely know that you will only ever want one certain size. Crop for aesthetic reasons, but save all the rest and make a cropped copy when it comes time to order a print.
Elie

People order photos in whatever size they want, I crop to the size they want and have it printed. You can't automate cropping, and cropping all pictures to all sizes isn't practical.

So I guess my question is: Do most people save the full image and only crop when it is necessary?

Sometimes I crop for creative effect, but i'll usually keep it to a 3:2 ratio.

I do. I'm going through a large project of getting a couple hundred shots ready for print, and I never know whether I'll do 4x6 or 8x10 or 5x7... They all crop differently. Sometimes I'll do 2 sizes of the same print and see if the larger one looks good enough. The variations in sizes - and the resulting composition possibilities - mean that I now process full size and crop off that.