Another reason why some home roller sets might not come out as well as the salon may be due to the amount of tension you apply to your hair while rolling it.
I went with BRH to get hair rollerset last Saturday and the gentleman rollersetting her explained the effect of tension, using rollers that give good tension, using end papers and securing the roller.
As he set each piece of BRH's hair, he first put a end paper on the bottom and top of the hair section. Then he slowly pulled it down her soaking wet hair and simultaneously rolled her hair using a good amount of tension. This is an advantage over any at-home roller setter because he was hovering above BRH and could get the right tension on the roller. He also rolls very quickly and told me that as he is pulling the end papers down the hair, the hair is getting smoothed by the end papers and by the time he puts the roller in and secures it with a pin the hair does not even have a chance to wave/curl back up.
He also mentioned that he uses straight pins rather than clip to tightly secure the rollers to her head. All of those element equal a smooth, straight roller set.
I will try to do some of the things he suggest. But I do relalize that I may never be able to create the same amount of tension he does and I don't use the straigh pins very well. They seem to "cut" my hair when I stick them through the roller.