They don't teach marketing in tafe or uni. But they should, considering its the first thing you do before you do pricing, product, services, etc.
Word of mouth is a form of marketing. Referrals are marketing. "My quality of workmanship speaks for itself" is a form of marketing. "I don't need to advertise, I've got plenty of work". Good, you're advertising right now. You're advertising that you don't advertise. You're trying to sell me on the idea that your this special unicorn business that doesn't need to do marketing. Everyone is engaged in sales and marketing. Don't treat it like the boogeyman, it's vital to business!
Marketing is attention. Don't let the marketing pencil necks tell you to it's about getting found when it matters. I want to get found when it matters and when it doesn't matter. No energy spent on marketing is ever wasted. You complain about low quality leads, timewasters, but that's only because you don't have multiple entry level offers and ascension.
Look, as a tradie you have so many marketing tools relevant to you. Site signage, vehicle signage. Word of mouth. Google. Social media is one of the best ways to gain attention. Guys are like "Oh I don't need a website Alan, I've got social media." Good, put a high performance website on it and it'll get even better. This is about branding. This is about customer experience. All roads lead to home page. Make it a good one.
You want to use all the marketing tools at your disposal, and you want a professional handling your SEO. You want to make sure you have a proper built website, because you'll have trouble ranking a poorly built website in Google. You'll get a cheap website and end up paying way more in SEO work later down the track, than if you had a reasonable budget in the first place.
Marketing is attention. You want to explode.