Items:

another thought about the blind auctions... maybe each person can submit an item for the auction to get it started, and new items are generated as the first are sold around the power level of the average item... so you could try to sell worthless/cursed junk but then you would only find worthless junk generated to mix with your worthless junk...

NPCs bid for items?

Loot captured by NPCs put up for auction?

Techs:

I'd like the bidding to happen this way for the fight over who else gets 'deathbows'... but I would rather a sword of the stars style tech trading, you gain the option of researching/funding 'strange new thingy' over a few turns... to allow you to research 'new thingy' (making it now green rather than red or non-existent or if it was already green you could gain it instantly) so there's still a set gap between the trade and you having deathbows, unless you would have been able to research them anyway next turn.

Sounds good to me.

Do you mean mercs as in heros or normal soldiers?

slightly off topic from auctions... but with mercs... should you buy them, a group of troops you use like normal troops or fodder... or should you buy the ability to use them? Say if you win the bid you can summon them 3 times, you select where you want them and they go there for 10 turns... so instead of just getting free troops you get to send troops where they're needed for quick boosts to defence or attack. To avoid using them as fodder, maybe you have a cost to hire and a life insurance cost, so you pay for each troop that dies, a small amount but something to make you think twice about just throwing them against the enemy all the time.

(reading starcraft 2 campaign you can hire mercs, upgraded from normal troops with no build time for instant boosts... I just think they need a time limit with some deterent to stop you using them as fodder... maybe you can only summon or hire them again if the controlling NPC of the group survives? either that or increased costs for use as suicide squads)

I think faction relations could work... I was just thinking that you would need multiple merc factions that way... at least a fallen/kingdom one... or you would be able to hire trogs if you previously bought several angel defenders... if you split it into multiple ones then you could probably get away with hiring from each and using them all as suicide squads (and you would barely increase the costs with the more different factions). I suppose you could lower trust with all merc factions if you kill them within a few turns of the contract expiring... and only gain trust with the faction you buy from.

I don't see why multiple factions would be necessary.  Mercenaries would all be in it for the money, with the goal being to make as much of it as possible without getting killed.  Your faction relation with mercenaries will simply be a metric to judge how good you are at paying your mercenaries on time and not getting them killed in excessive numbers.  A Trog mercenary commander who just watched you massacre your 1500 human mercenaries or failing to pay your mercenary archers is probably going to either refuse to accept your bid, or require a much higher price, regardless of the race of the other mercenaries you hired.  Simple self-interest should dictate behavior regardless of race or affiliation.