i dont build finished arrows commercially- just my own for personal use, but i sure talk to a lot of pro builders, and over time have figured out a system that works for me. so be warned it may not entirely be the way the pros do it.
1.all wooden shafts will need straightening to some degree, so i look down a fresh shaft and see which end is naturally more straight than the other- thats the end i put under the fletches. i mark that end, or put on the nock taper. its the part of the shaft thats least likely to go crooked again for any reason, and straightening a shaft around fletching is a real P.I.A.
2.i give the shafts all their first go around of straightening.
3.then i stain, if i am going to, that really helps to make the grain "pop" helps me to see the best way to orientate the shaft
4. first coat of sealer- i just use water based poly
i find the biggest contributing factors to an arrows straightness, and maintaining it are temp and humidity, i get that first coat of sealer on, and try and put an end to the humidity issue.
5. second round of straightening, and maybe will do a third and final tweak if need be, and second coat of poly.
by now the shafts should not be moving anymore, and should be nice and straight- checked on my spin tester.
6. cap dips and cresting etc.( if i am going to- but usually not)
7. last coat of poly
8. fletch
i use a roller straightener to straighten my shafts, personally, i think its the best, and it hurts the shaft the least, but can leave dull spots on the finish- so that why there is one final coat after all the straightening etc.
I stump shoot with all my arrows, (and we live in a coastal rain forest here, so its always raining - just the angle changes!! ) and i have shafts that i have shot many thousands of times into brush at stumps and dirt, and i find if properly straightened, and properly sealed, i never need to re-straighten them again.
i know this is more than was requested, but thats how and when i seal.
and i use a simple water based poly.
But then i dont 3D or target shoot, so target burn is not an issue for me.
many folk who are concerned about target burn, seem to have a lot of success with " Dalys ProFin"