You would hope that expensive shirts have finished inside seams but that is not always the case. The inside seam should be flat and smooth. I have some Ibex light weight wool shirts and they have wonderfully smooth inside seams.

Three solutions:

1) just wear the shirt inside out
2) if you sew, buy some seam tape and cover the rough inside seam. Use the seam tape that has little folds on each side. Seam tape comes in both synthetics or cotton. Not sure the shirt is worth the cost of having a seamstress do this for you.
3) wear a very light smooth tank top, inside out, under the shirt, if you are freaked out by others seeing you wear visible clothing inside out.