I used to burn nothing but pallets for yrs, I stlll have a giant stockpile of pallet slats stowed away.
The only pallets you should avoid are ones that stink, or are covered with mystery stains, greasy, or overly painted ones.
and the repaired ones that are full of staples and nails are worse, they ruin the chainsaw.
I have a few places that repair pallets here, so quite often there are truckloads of nearly new pallets for free sitting out. Anything that isnt 48x40, they dont want.
In fact I bring them a load of 48x40's and if they are in decent shape and only needing a slat or 2 repaired, they pay me for them!
I used to get $2 for each one, I have sold any in a few yrs.
As a bonus, now and then they get skids of new, clean pallet slats and bars that are the wrong size, and they toss em out. NO NAILS
! Virgin pallet parts!
The last time I scored there I got THREE full skids of what seemed to be poplar planks, 1/2" x6" x48" they ordered oak and got those, and man, I had the best stash of kindling for a few yrs.
Once I got a whole truckload of warped 4" long 8"x 1" planks, I think they were pine. they burned really nice.
Find a pallet recycler and become their best friend.
But there is one place near here they grind up pallets to make mulch, I drove in and ask em how much for a load of crushed pallets (the crush them then dump them in a giant thing thats like a food processor... its really cool) and youd a thought I ask em for free gasoline, they scowled and almost chased me out the door.
I probably was the 500th person that day to ask that same question.... I dunno.
But the places that rebuild the pallets to resell ALWAYS has scrap. A lot of it is broken slats and rails so your job is halfway done, you cart off their garbage and they love you.
We used to have a box and crate company here too, they made shipping crates for machinery, and had 2 big hoppers full of cut plank ends, 2x4 pieces, odd scrap and now and then, bundled wood they didnt want. They went out of business, and I cried a little. LOL