It looked as if you cannot get more than two. The first 2 luckies, I got them 1 in 7 or 15 trades. After that, I traded all the way to daily limit, and never get anything. I have done the trades for many nights now, and observed the same pattern. Get 2 luckies early on, then nothing after, even if I traded 70+ trades consecutively, nothing.
For the first month, about 15% of my trades were Lucky - though the first 20 or so were terrible. (My first two Lucky's ended up being a Larvitar and a Tyranitar that were traded for Candies. HA!) Nearly all of them were between 67% and 81%, and really were more annoying than useful. (the above two being the exceptions to the rule)
Since then? Maybe 5 Lucky's out of 200 trades. I'm back to trading for Candies again.
I got 3 luckies, the 3 sinnoh starters, by trading with a friend between 25/30 mons (and before that i got a lucky Beldum the same day trading with other guy) We did it walking from one raid to the other. Maybe it helped we were best friends in game but i don't think there is a daily limit on luckies you can get or any real way to boost your lucky chances besides how old the Pokemon being traded is, it's pure RNG
When lucky pokemon were first introduced with a 10/10/10 IV floor, I saw about a 10-15% lucky rate.
When they bumped the IV floor up to 12/12/12 and added the guaranteed lucky method for people with less than 10 lucky, the regular lucky rate dropped to around 5%. Somedays better, some worse.
Supposedly trading older pokemon improves lucky chance, but everything really special (shiny legends, legacy moves, etc) that I decide to trade for a 2016/2017 has been unlucky.
It's really random. I'll do 10 trades a night for 4 or 5 nights and not get any. Then I'll do 5 trades and get 3 luckies out of them.
On beldum day for example, my gf stopped to go to the bathroom and gave me her phone and I traded 5 beldums between us - 3 of the 5 went lucky. Then during the extra hour we traded about another 40-50 beldum and not a single lucky.
