You can try to accumulate money and buy a full build at once, you don't have to buy everything in the shop

This is one of the problems I have with super mechs..

The point of this game is not just fighting, it's strategy
You need to plan ahead, you have to think what would be good with a torso(especially this, since the torso is the core of your build, a lot of things depend on it), module, weapon, or something else. you will need to examine each item properly for the build you're planning(you can choose a level to build your mech at, it can be higher than your own level if you want to), and decide what would be the best for you, hold that in your mind, and buy when you can. if you have bought the wrong item, you can sell it for a full refund if you don't exit the workshop. NEVER EVER SELL YOUR OLD BUILD UNTIL YOU CAN COMPLETE YOUR NEW BUILD WITH THE MONEY YOU GET FROM IT. Also I wouldn't recommend to sell your old build even if you can get the new build. There is a chance that it might not work well, and by selling your old build, you'll lose your credit source if that's the case.
So, a summary: don't buy a lot, never sell what you have bought(unless you still can get a full refund) and plan what to buy.
I understand you concern, I really do, but think about this: If anyone was able to sell everything with a full refund no matter what, than the game would lose some of it's depth. this feature is put to make the players think more about what to buy, since this makes it more strategic.

Whoa that was a long post...
Hope you can understand what I mean, cheers

I think I've misunderstood your point before, sorry about that and thanks for making it clear
Current refund price of the shop is %25 of the purchase price, and this is not enough to test a weapon, that's a fact. And there are a lot of people suffering from it. There has been some topics with some ideas about solving this problem, I'll give the link of one of them here, which I find useful instead of increasing the refund price.
Here is the link:Click here
I hope that you'll like it too.
Edit: Until this is solved, you can do as I said in my previous post, this way you can avoid it as much as possible...
But be careful choosing your build, because if it fails, you might need to change more than just a weapon...
Cheers