What's your way to validate the need for a product before building it?

You mean before creating it?

I personally think if there are multiple competitors in the market you want to dive in, then the product idea is already validated. You just need to worry about how to compete with them. If your idea is pretty new, then search over communities and forums and listen to what people says about the needs and wants you want to fulfill can help you a lot not only to validate but also to develop your idea.

Here are few things which might help you: 1. Create a form and populate in targeted community 2. Talk to experienced people in the industry 3. Look at Competitors 4. Create a landing and run FB ads

Can always create an MVP landing page, something that illustrates your idea and create a waiting list or pre-order list. If you decide there's not enough validation to actually create it, you can refund your pre-orders.

With Sense (will launch on PH soon...), my strategy was to create a MVP as quickly as possible and get my first sale. Within a week I had a MVP up for the first interation of my app and got my first sale (manual collection, no billing system as that takes time). Within another week I had another, so I knew I was onto something. The key here was not to spend a lot of time 'building it', though in response to your initial question I still built it. I think it's helpful to have something to show people before they purchase, but if you find a pain point large enough (especially B2B) then you can pre-sell solutions through conversations. I think that'd be harder to B2C industries. I also validate my ideas by using them myself. If I wouldn't use them then why would I build it, or believe in it, or care? But after that a few more sales from a consistent profile should do the trick.