There has been a rash (and yes, they literally make me itch) of articles lately that have contained run-on sentences. Run-on sentences are characterized by the omission of punctuation to separate clauses or complete sentences from one another. Run-on sentences have no place in professional writing and are easy to avoid.
If you're in doubt about whether or not the group of words you have written is a run-on sentence, simply break it up into two sentences if each part can stand on its own.
Incorrect:
You may find it difficult to house train your small dog, they have small bladders.
When you go to a mortgage broker keep in mind that he or she will run a credit report and be sure to ask him or her about how that will affect your loan.
Correct:
You may find it difficult to house train your small dog. Small dogs have small bladders.
When you go to a mortgage broker, keep in mind that he or she will run a credit report. Be sure to ask him or her how that will affect your loan.