biscuit mitre joints / set up of CMS

I am pretty much a newbie but have some cool tools to play with, one being a biscuit jointer. I've done a few panels and shelf faces, but when I followed my Wood plans for making the base of a bookcase and it showed the trim with a 45 deg biscuit, I looked at it carefully, and cut it out fine. Dry fit just so fine too. Sweet. Then on assembly, the old swelling biscuit from the wood glue reared its ugly head. It was very tough to get the parts to go 100% together as they did dry. I think I got like 98 or 99 %, but it was tough to push parts together that were at a 90 mitre joint, and clamps were not any help. Any sage advice on these? The joint looks ok and is not really noticable, I did use a bit of the wax stick to fill it in just ever so slight, so it could be better.
Also, in a somewhat related topic, my purchase of a used dewalt 12" sliding compound mitre saw, I did a check of the blade at 90 with a square and all seemed good. Then when I cut some 45 mitre joints on tall parts, it was obvious it was out a bit. I then cut 45's on more scraps and used a square to adjust the angle of the saw to get it to 90 from horizontal. I think I got it pretty close to perfect, and I discovered that cutting two mitre parts, then setting them up on a flat surface and measuring to see if they are 90 deg from the table seems to be a good way to setup a CMS. Is there a better way, w/o expensive gear? It occured to me a toothless blade would also be a decent way to set it up.

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