It’s funny how the OP specifically asked for methods
apart from VPIP and bet sizing, yet half the replies are still just saying "limping" or "watch the VPIP" lol.
Since we are strictly ignoring stats and bet sizes, my number one method for these daily games is just watching how they use the chat and the "show cards" button.
If a guy is writing paragraphs in the chat about how the RNG is rigged because his aces got cracked, or if he voluntarily shows his folded cards just to prove to the table he made a "sick laydown", tag him immediately. A solid reg eats the bad variance in silence and hides their information. A weak player plays entirely with their ego and is usually just one bad flop away from a full tilt meltdown.
Also, Kasztor007 is completely right about timing tells. The post-flop snap-call is the ultimate weak player signature online. If the board is wet and you fire a c-bet, and they call in a literal fraction of a second, they aren't thinking about your range or pot
odds. They just looked at their own cards, saw middle pair or a gutshot, and mashed the call button. A thinking player always takes at least a couple of seconds to process the spot