My biggest complaint is writers who do a poor job of checking to make sure their facts are correct. Because when they fail its hard to suspend my disbelief on the rest of the story as needed.
What do I mean. Well in order for the reader to believe your plot often involving unlikely situations you need to ground a story in as many true facts as possible. eg If you are writing about London in the 1900s figure out a few details that place your reader there. And get them correct. Now I recently heard this from a main stream writers who has over 40 published novels. When he reads a book and finds details that he knows are wrong he starts to question the premise and the story itself. For me that is even more important here in SOL when a lot of the settings like family sex parties or sexy time travel. Know how a pistol works if your character uses one; know who the President is or when a great war started. Giving the reader a believable world will create a better story allowing the reader to believe in you no matter how far out your plot.
All this to say search engine is your friend and the tubes. Use them.
And writers don't get in a huff when people tell you your facts are wrong. Make the changes, if you care.
End of rant.