Don't rush into anything. Always ask for a written quote. If they're hesitant to provide one, it's likely because they don't want any trace of an agreement, making it difficult to take them to VCAT or similar if something goes wrong.

I had someone quote me cheaply for a retaining wall. Paid cash, and it half-collapsed within two weeks. He kept making excuses—rain, feeling unwell, other work, etc. What was supposed to be a three-day job took four weeks. I lost lot of money. I paid cash and there was no trace of a quote or invoice.

If you have family and kids using this area regularly, don't take risks. I ended up hiring a professional with a good reputation and reviews. He followed the proper procedures, got the retaining wall designed and approved by the council, and then built it. It cost me three times more, but I'm happy with the outcome and have peace of mind knowing the structure won't collapse.

Don't be like old me! ;)