How to justify a reckless decline properly?
Justify a reckless decline in a public tender ... Uff, that's not anything. You have to curb it well, because those who check those offers do not suck their finger. When you get ready and send an offer with a ridiculously low price, those of the public body will ask for explanations, yes or yes. And eye, each tender has its own "personality": there is no universal manual, because the rules change depending on the country, the city, the planet (well, not so much, but almost).
First of all, here is not "trusting me, bro". The test is on your roof. You have to demonstrate with real data and solid arguments that your offer is not a suicidal madness - that you can meet that price without the project ending up being a fudge. As? Well, showing your cards: you still have your own factory, a technology that nobody else has, or you are simply a crack optimizing processes and saving costs where others do not even see it.
Sometimes, the trick is in the economies of scale, or in catching very good suppliers, or because you have surplus in stock. If you have a magical app that automates tasks and reduces labor, teach it. But nothing blah blah: you need concrete details, not promises in the air. Explain how you are going to save: Do you have suppliers that make you a friend price? Does your team work at the speed of light? Wholesale purchases and give you shipping? All sum.
In addition, do not forget to document everything. You have to go with tests under your arm: reports, balances, contracts ... whatever, but it is seen that you are not invented. And, of course, review the regulations of the site where you are introducing yourself, because they ask you very specific things (in Spain, for example, the Royal Decree that famous makes it very clear: if you do not justify, they send you home).
So, summarizing: justifying a reckless leave is not just a matter of "I make it cheaper." You have to sweat the shirt, demonstrate with papers and arguments that your offer is viable and, above all, adapt to what each tender asks. If not, not even try, because they are going to catch you.