Influence Enhancives and Trading

[Bumpur]

Let's say I have trading skill (10 ranks) and I wear enhancive items that give me a bonus to influence (+20 bonus). Do I use up a charge of each influence enhancive each time I sell a gem?

I'm asking because I have influence items which can put me to a +20 skill bonus, but I currently have 0 skill in trading. I am considering training in trading, but will not do so if it's going to eat up my influence charges which I need for combat.

[Archigeek]

There's a very good summary of trading, including how the formula works and how it would help you, on Krakiipedia.