... and three other tricky workplace dilemmas. BY ALISON GREEN for Inc. Here's a roundup of answers to four questions from readers. 1. My client is always late paying me One of my clients, a creative agency, has always had issues paying my invoices on time, but it's getting worse. Every single time I send an invoice, I have to go back and remind them to pay me. It's a great company, but I'm starting to get frustrated that I can't send an invoice without having to follow up repeatedly. Sometimes they say they missed the invoice, sometimes they apologize, but I eventually always get paid.…