How much to tolerate is up to you. If it is a very small dent, then you can leave it alone.
For removing dents, it is important to know the bore size. I have made aluminum plugs in 10 ga. 12 ga. and 16 ga. that are in .002 increments. I insert them into the bore to find the size up to the dent. I then make a steel plug that is .002 smaller than bore and tapered to slide under dent. I then lightly heat the area and will then tap the plug so that it is now tight and then use either a brass flat head hammer if it is a large dent, or a flat head hard plastic one. I then tap the steel plug more and keep doing so until plug slides past dent.
This plug gage is for a 10 ga. that has a bore of .775.
This barrel was ready for rusting/etching, and sometimes if the bluing is good and the dent is small, you can get away with not re-bluing whole barrel.
