IV reroll testing- bad rng or am I missing something

For UF the iv reroll is random with a floor of 4, just like weather boost. As to level difference, if you traded him a mon higher than lvl 34, which is the highest level he can power up to, it will go down to 34. Otherwise it doesn't make a difference. I had a rattata go up to 93% in a trade once.

From The research done i believe The floor is 1,2,3 and 5 increasing with friend lvl.
Dont expect any mons to gain IV, People Who far exceed me in math have calculated a 3-4% chance of gaining a 95+% IV from trade.

I did about 50 traded with an ultra friend today. Secured a 95% corsola and 97% squirtle. The corsola had bad IVs and then squirtle was unknown. My friend got one 93% out of all of it and some some lesser wonders too.

Like others have said, it's not like the odds are good. I've done 860 trades and gotten a grand total of 3 good IV mons worth saving from it. Often an entire 100 trade session goes by without a single good one for either player.

Trades of note, right now I'm holding off til lucky pokemon confirmations:
These are ones I've kept from some earlier trades and ones done first day of ultra; overall more became worse ones than better outcomes (done 427 total trades, lots trashy ones, giving stuff away, grinding candy, getting pilot miles):

Had a Level 35 Snorlax go up 2987 to 3029.
Level 30 Dragonite (ultra) started bad, like 2890 (a 1 stamina) went to 2948 12a/6/6; think Dragonite on the other end went up a bit, too. Vaporeon level 35 (ultra) went from low 2700s to 2888--appxm 15a/11/12. Level 29 Smack Down Tyranitar (ultra) went from 2901 to 2994 14a/14/11. Level 12 Blissey went from 980 to 1089 15a/12/15.

I've done only 34 trades in total, and had a reasonable handful go up in iv. I'm talking like from 50 to 70. We've both gotten at least 2 that went over 80%.

It's random, and not great odds. They'll happen sometimes though.

As far as we know, it's a re-roll. Trading with best friends gives a floor of 5 on stats, nowhere near as good as eggs, raid encounters, or research encounters, where the floor is 10.

But let's be real, you do a Machamp raid, and get a 11/12/10 (ads, although it doesn't really matter). You're never going to power it up or use it, given that you can do 2 more raids and have a 99.9% chance of getting a better one. So trade it to a best friend, and the chances of them getting a 90% or better are:

Best friend = 35 in 1331, or 2.63%
Ultra friend = 35 in 2197, or 1.59%
Great friend = 35 in 2744, or 1.28%
Good friend = 35 in 3375, or 1.04%

Want to do the math yourself? There's 1 way to get a 100%, 3 ways to get a 98%, 6 ways to get a 96%, 10 for a 93%, 15 for a 91%, 21 for a 89%, etc. Add up all the combinations for the group you want (90%+ = 1+3+6+10+15 = 35 ways), and divide by the total number of possibilities (for Ultra friends, 5-15 is 11 possibilities, and 11^3 = 1331).

Most trades were just fodder or regionals, I don't know what their IVs were before trade. I've had some relative good luck with a couple though:

L31 Larvitar: 14a/5d/15s
L29 Beldum: 15a/single digit rest

For being as high-leveled as they are I'll gladly keep them thanks to their attack IVs.

I have had luck with only two trades so far: a 100% Alolan Meowth and a 96% Mr. Mime. Everything else has been trashed.

I’m kind of annoyed that the floor doesn’t go to 10/10/10 at Best Friend status. To me, a 5 is no better than a 1; I would never power up either. And it’s for that reason I’m in no hurry to trade legendaries. I really wanted a TS Zapdos since I missed the event and Niantic made the boneheaded decision to TM lock the fast move. But I’m not spending the dust with the current odds. I’d honestly rather not have one than get one with 5/5/5 stats.