I've been wondering something and perhaps you folks know the answer.

Does selling in bulk raise the Speech skill more than selling individual items?

Let's say you had 250 blocks of firewood. Would you gain more Speech if you
sold them all at once or one at a time?

To put it another way, would selling say potions individually at 10 septims
raise the Speech skill more than selling say 10 potions at once for 100 septims?

I think the more money you make in transactions, the more speech skill increase

From what I understand, no. To increase your speech skill quickly, sell in multiples of one. If you have 530 arrows, selling them one by one gives you more skill than selling all of them at once will.

Also, you really shouldn't sell firewood. Just bring them to a logger guy because they have infinite caps. Save the merchants gold for more important items.(unless you're trying to raise SPeech, that is.)

if you sold them all at once, you only get the speech experience of selling one. With cheap stuff though, you are better off selling them all at once cause it would probably take awhile otherwise for not that much skill gain. Speech skill gained is governed by the price of the item. Even if the vendor is out of money, you still gain the speech experience for selling it.

I just tested this out with potions. You are correct. I sold 9 potions at once and I couldn't even tell that the skill increased at all. Reloaded the save and sold each of those 9
potions 1 at a time and it was an obvious increase in the speech skill.

One at a time. You get xp for both the value, and the number of transactions from what I've read.

Oh ok, that's interesting. So, what you want is a lot of a good priced item. Well, I say good priced
meaning an item that a merchant can handle a lot of transactions without running out of money.

You get money for buying stuff too.

Restoring the thieves guild helps in finding high money merchants.

One at a time. If you sell them in bulk you will only recieve the experience for the value of ONE item. Always where possible sell items individually. But only if they're actually worth a lot of money to begin with.