Even though Gon was clearly aware of Blue Flame's ingrained arrogance, he still required his prowess.
3rd tier guilds weren't like the guilds above them; they were much weaker, be it financially, strength-wise or even the number of competent folks when compared to the latter. Lacking financial abilities comparable to real 2nd tier guilds and above makes it difficult for them raise a blacksmith from scratch so they usually resort to hiring a freelancer. Having their own blacksmith would help them cut their weapons budget by a lot and it could help them gain a good foundation at this stage in the game. If they make use of the opportunity correctly, they could surpass other 3rd tier guilds and maybe step into the rank of 2nd tier.
"Brother Blue Flame, whatever you need to be done here or collected, just ask and my me shall help you."