Builders in Mango Hill, QLD with e-mail

I was hired by RPG Builders to design their new office premises at North Lakes. I quoted a specific figure and clearly stated that my terms were 50% deposit to commence the work. I was paid a percentage of the deposit with the promise that the balance would be paid "within a few days". Despite not being paid the full amount, in good faith I commenced the design work. During this time, I was also asked to perform other duties such as organizing quotes for partitioning from different suppliers and also to give them a list of suppliers for various building products. I did this at not added cost to them. Whenever I would text or email about the balance of the deposit, I was fobbed off. This went on for three months, despite the fact that I had given them a first draft. It was only when I advised the director of this company that unless the balance of the deposit was paid within 24 hours, I would have no alternative but to engage a collection agent, that they paid the balance of the deposit. My advice for anyone providing a service for this company is to proceed with caution.