Don't get me wrong here, as I'm with you, it can be fuckin annoying AF not to get a straight answer quickly so you can assess and make decisions between suppliers.
But that's also part of the process from their end when you actually are talking with a manufacturer, they are not looking for quick $, they value long term relationships/partnerships.
But, its a cultural thing in China when you actually are dealing DIRECTLY with a manufacturer. They are HUGE on building relationships, you start out as some random customer but over time you build a relationship and if you're ordering in quantity (no matter the industry/sector) and you start going over to visit their factory... Its like you become part of their family over time! They will literally bend over backwards to help you at that point! Their entire company culture is built around this core concept of building long term relationship's!
Once you get your head around it, its actually a really nice thing to find in trade/commerce! You see it to varying degrees in a lot of countries when dealing directly with manufacturers but Chinese people really take it to a whole other level!
Got to understand that most of the suppliers we see or are on any of the China manufacturing portals, are mostly resellers. They have the language and feet on the ground to go to the manufacturers, build relationships and get amazing deals that then allow them to make huge markups setup as a wholesaler. They don't care so much about relationships with the end customer, its all about churning volume so they can access the pricing at their MOQ with the manufacturers.
As annoying as it is, it lends weight to this sources claim that they actually are a manufacturer.