are all used LPs dusty?

Quite often YES. A record cleaning machine or regime of some sort is a must even for new records, check the archives, there is plenty of info there

A record cleaning regime, as uru975 put it, is essential.

Before using a record cleaning machine it is a good idea to let the record rotate while you use a dust/particulate matter remover such as the venerable Audioquest carbon fiber brush, or one of its competitors.
This picks up the dust, then you clean the brush by rotating it against its own built-in straight edge so the dust flies off the brush (pointed far away from the record you are cleaning.) Usually one needs to repeat this two or three times until you see that no more dust is visibly accumulating on the brush.
This removal of original record surface dust or fine particles prevents contaminating the edge on suction tubes of record cleaning machines such as the famous VPI 16.5

Some are not but it doesn't matter.

If you want good results with used records, you have to be prepared to clean them properly first. There is lots of info here on A'gon and elsewhere already regarding various effective ways to do this.

Otherwise, stay clear of used records in general. Its hard to tell by visual inspection if a record is really clean or not.

Generally yes. The paper sleeves have a tendency to crumble and that leads to dust. A lot of good tips on cleaning posted, but don't forget steam cleaning as the best answer.

I use one of these. I use a carbon fiber brush for touch up before playing.This system works good for me.

1) Yes and no. New or used, all records benefit from proper cleaning. Cleaning not only improves the sound, it reduces the chance of permanent groove damage which can result from dragging a diamond chisel through a plastic groove filled with (microscopic) bits of junk. Much safer to drag the chisel through a clean groove.

2) Wet cleaning and vacuuming. Other methods provide some improvement, but you asked about the "best" method. Cleaning without wetting is an oxymoron. Wetting without vacuuming away the sludge just rearranges the sludge.

3) Cleaner? Probably. Clean? No. The dirt that matters is deep in the grooves. It cannot be seen without a strong microscope.

"Wetting without vacuuming away the sludge just rearranges the sludge. "

True vacumming is the most common solution I suppose.

I have found that using tightly folded edges of a very soft and absorbent paper towel like a record cleaner while the record is spinning does a very good job of removing excess solution when cleaning a record.

I've been doing this with good results using my Linn Axis table now for a good 25 years or so.

I use extremely dilute Shaklee Basic H cleaner in water, distilled water is preferred if availble.

I spary the record surface down thoughourghly, place teh record on teh table, give it a good scrubbing with an old discwasher brush, drying the discwasher brush periodically as I go using another absorbent paper towel as needed.

Then I use the paper towel technique above to dry the record.

Once you develop the technique, is is inexpensive and most effective with only one pass and only takes a couple minutes per record side.

Anyone know how to assess if a record is going to be noisy due to groove damage by previously bad needles? I've been disappointed a few times buying a used lp after judging it "very clean/near mint" in the store's light but discover at home bad static like background noise rendering the disc unlistenable. Now I recognize it's one of the risks in used lps hunting. One clue I look for is the amount of impressions around the center hole of the label. If there's a lot of tracks around it, it tells me its been played a lot so I might downgrade it among my decision factors (price, pressing, rarity, etc...) in purchasing it or not. Finally, if anyone has any tips to spot "noisy" records that look clean-good, let us know.

Anyone know how to assess if a record is going to be noisy due to groove damage by previously bad needles?

IMHO,the only way to know for sure is listen to it.I have LPs that look totally trashed and sound excellent and brand new ones that look,well,brand new but sound like crap.I'm sure there are some folks that claim they can tell just by a visual inspection but I don't believe it.Just call me Doubting Thomas.

I recall a product in the late 70's/early 80's that you were supposed to spray on vinyl to 'protect' it. It left them very shiny, as if ArmorAll'd, but made them noisy due to trapping existing dust, as well as leaving behind microbubbles. So much for shine vs. functionality.

You'll thank yourself if you get a VPI HW 16.5 record cleaning machine. You can buy them used for @$350. And sell them used for around $350. It's like buying basic tools if you're going to rebuild the brakes on your car.

PS-pls. don't "wipe a used LP with a towel"......

Only 90%.