I use approximately the following scoring system for trade offers on the League of Impatient Cave Cleaners:

Score break-down

Starting score: 7

Offer

1. +1 for every caveblocker species hatchling offered
2. +0.5 for every other hatchling offered (unless it’s so rare that I decline the offer)
3. +0 for every egg offered (unless I’m egg-locked, in which case it’s a decline)

Trophies

For rares:

1. +0 for no trophy
2. +1 for a bronze trophy
3. -1 for a silver trophy
4. -2 for a gold trophy

For non-rare caveborns:

1. +1 for no trophy
2. +0 for a bronze trophy
3. -1 for a silver trophy
4. -2 for a gold trophy

Visibility

1. -2 if adults / frozen hatchlings on scroll are not visible
2. -2 if eggs / hatchlings on scroll are not visible
3. -7 if scroll is entirely inaccessible (no trophy visible; does not stack with other implicit scores)

Uniqueness

1. -1 if you already have a dragon of the species I’m offering
2. -1 if any of those dragons are equally clean or cleaner in lineage than my offer

Examples:

• Bronze-trophy scroll (+1) with no silver offering 1 caveblocker hatchling (+1) on a 2G silver: 7 + 2 = 9
• Silver-trophy scroll (-1) with CB silver (-2) offering 4 caveblocker hatchlings (+4) on a 2G silver: 7 – 3 + 4 = 8
• Gold-trophy scroll (-2) with CB silver (-2) and hidden eggs/hatchlings (-1) offering 4 non-caveblocker hatchlings (+2) on a 2G silver: 7 – 5 + 2 = 4
• Invisible scroll (-7) offering only eggs: 7 – 7 = 0

Only the relative score is important (i.e. no score is declined on principle; though the maximum possible score (12) is auto), but once I have more than two offers I start declining those that score lowest, to save everyone time. <3