I don't like spamming something in general, but I wouldn't stop it. I would do one of two options though.
1.
P1: this is what I want to do <snip>
GM: ok, roll.
P1: didn't get it.
GM: ok, that's your character for the day, everyone else, what are you doing?
P2-5: we're investigating those leads.
<two hours of gameplay later...>
GM: Ok, P1, it's the next day try again....
P1: <sigh>...
2. Taking a hint from my d20 days and the roll 20 skill options I would calculate the odds of success and the maximum time. For example 1Y has a 1 in 12 chance of a triumph. 2Y has a 1 in 144. So If you needed two triumph it takes you 144 tries. This represents someone taking their time and working towards something without rushing and no chance of catastrophic failure. If it takes the character a year to make it, then so be it. There's a reason companies have entire teams of engineers working years on new projects. One character, no matter how talented, would take a long time unless they wanted to go with option one above.
As far as selling off unsuccessful attempts, I might give 10%. Because this isn't about making the same thing over and over again and learning to do it better, it's experimenting and prototyping on how to make something better. So the character would have unfinished copies and attempts that didn't work out. Some, would be functional enough to sell normally to the open market like any other collected gear, but a lot of it would not be.