Old receivers can work, depending what you want to use them for. Maybe fine for a simple 2ch setup. They're not magic, tho. They may need service, sooner than later (and if you buy one that has been refurbished that tends to take any "bargain" out of the picture). They can be more repairable than some new units perhaps, if you can find someone still working on such but then there's the expense of the repairs. They tend to be analog only so to use digital media with they're going to need help. Do you even use AM or FM radio any more? They're popular to some degree due to hands-on knob feel and glowy lights that is nostalgic to some, I suppose somewhat like vinyl....touchy feely experience that some miss with digital media.
OTOH I have no idea what you mean by tweaked.....