About
Most idea validation is built by product people. I come at it from sales.
I'm Tomislav Kostanjevac, founder of Will They Buy. For over a decade I've led B2B sales, building teams, launching products, and opening new markets. The truest test of an idea isn't a survey or a workshop. It's whether someone will pay. That's what I help founders find out, before they pour in months of work.
Tomislav Kostanjevac
Founder, Will They Buy? · Co-founder & CSO, Dishboard
"The only validation that counts is someone willing to pay. Everything else is an opinion."
10+
years in sales leadership
€1M+
ARR startup co-founded
20+
founders advised
My career has been in sales, mostly in leadership. Building teams from nothing, launching new products, and opening new markets.
It started at Dish Digital Solutions, one of the largest hospitality platforms in the world, with more than 300,000 customers. I built its first sales team in Croatia from scratch, then moved into an international role, opening new markets and launching products across them.
Today I'm a co-founder and CSO at Dishboard, a B2B startup we've scaled past €1M in annual recurring revenue, and it's still growing.
Alongside that, I've worked directly with more than 20 founders, from first-timers to serial entrepreneurs to established companies entering new markets. I help them prove an idea before spending on it, land their first paying customers, and build repeatable ways to grow.
Why sales, not product thinking
Most validation advice comes from product managers and design thinkers. It's useful, but it misses the signal that matters most: the truest sign an idea works is someone paying for it, and getting that signal is a sales problem, not a product one.
I approach validation from the commercial side, with real customer conversations, real buying signals, and real money on the table. And because selling is exactly where most founders freeze, I also help you get genuinely comfortable selling your own product or service. That's the loop most programs leave open, and it's the one that decides whether you ever get paid.
What I believe
Selling is the ultimate validation
A survey is an opinion. A signed invoice is proof. I optimise for the second one.
Know your ideal customer inside out
Fast, confident growth starts with knowing exactly who will pay, and why.
I walk the talk
Everything I share comes from markets I have opened and the startup I run now. No untested theory.
Ready to validate your idea and test it in the market?
Book a free discovery call. If it's not a fit, I'll tell you.