What exactly the answer of the guild master means when asked "How is the trade"?

[Handel]

He says some numbers like Salt 1102, Iron 1016, Tools 1462... etc...?

 

[HolgerHardrada]

This is how bad the shortages are of a certain item.  In the example you gave, there is a rather big shortage of tools, while iron is not in that short of supply.

 

[SpittingLlama]

Question on that note, does that mean you would have to deliver ~1400 sets of tools to reduce the shortage? I assume that's a bit high...

 

[HolgerHardrada]

No, if you bring some tools or whatever in you'll see it drop down by a certain amount, not sure its a fixed amount or not.  If you bring in one tool that will probably drop the shortage 20pts or so.