Quality is important. Seldom do things go wrong with the processing of negatives. It is in the interpretation or printing process that occasional disappointing results are found. Amateur labs mass produce and print for a high level of acceptable prints. Subtle differences you may have made in your exposures are often cancelled in the printing process.
Any lab can have an off night.
So if you are not satisfied with your results, have them remade. Since there are not that many choices of labs, changing outlets may not improve your chances of quality. You may end up dealing with the same lab. Lastly is service. And by that I mean behind the counter because the processing service is the same.