You've done coverage for several networks and production companies. Work gets traded, talked about, etc. Wait a while if it doesn't sell right away and try your second choices. Know your characters inside and out. It's that simple.
Dialogue is a reflection of the character's background, birth, locale, and experience.
A prostitute in a big city just doesn't talk like a church-going farm girl. The Guild helps with health and retirement and, most importantly, tracks residual payments and enforces those payments. The Guild is also there to fight for you legally, if your rights are stepped on and there is impartial arbitration by your peers when a credit is questioned. It's a good group. Members are considered true professionals.