Correction: Transactions having many inputs which are change addresses reduce privacy. Wallets and sniffers can figure out which ones they are by seeing if it repeatedly appears as the second of two outputs along with repeatedly being an input with a bunch of other of similarly identified change addresses.
I think that most important when identifying an address as change or destination is the round/precision value.
For example, if you have 2 outputs, one is 0.01 BTC and the other is 0.00056721, the second one is obviously a change address.
Just having multiple inputs by itself does not reduce privacy, in fact that's how CoinJoin works. Inputs especially ones for addresses which haven't been used before don't give away any information.
Paradoxically, OP might have saw transactions that are part of mixers.
I agree that the number of inputs doesn't reduce privacy by itself. I have transactions from my signature campaign address that have 6-7 inputs from the same address lol
But the best practice would be to consolidate those inputs and send them to a mixer....
I believe small value inputs are a great privacy risk.. They do not reduce privacy by themselves, but they are a risk to privacy.
Signature campaign transactions are also a little "weird". They usually have 1-4 inputs and dozens of outputs. And each of those output addresses (the participants) have also uncommon transactions from those addresses, because each addresses holds dozens of inputs.
This is when we see bitcoin being used as real currency.
