Really depends and again it's all in the eye of the beholder. The problem is the time it takes to turn the stuff around and sell it. Are you just looking (and nothing against it, if it's at a recycler it's doom and gloom anyway right?) to flip vintage computers for profit? I'm sorta guessing that's your idea. Again, yeah some folks will flame it but hey, you're finding it at it's final grave site and getting it to a better home at whatever going rate there is.
One indicator is age of the device (always exceptions but consider pre-1988 is of general interest, the earlier the more interest) or visual uniqueness. Another may just be what you can afford to save and what you can afford to store for X time. If you can't save all the huge pieces that ya want (like you see all of us chatting away about the auction for 70 Commodore Pets). They're awesome systems but they're worth maybe $100ish depending on shape and functionality. Not too many of us have a few thousand to spare or the space/equipment to go take 70 of these full computers. If I saw one at the recycler I'd probably save it and know it's easy to get sold but shipping sucks so I'd be prepared to store it for a bit.
The more competent you are at fixing the machines and showing them work the easier a sale will be also. That's a huge tip for a successful vs unsuccessful auction/sale/etc. If you're confident enough that you think it will work (or if you're willing to fix it or list the problem it shows if not) you'll do well with lots of pictures.
Best of luck! It's quite a tough question and yes the gut feeling is what you'll need to follow. Some are winners, some aren't. Search for completed auctions on an item (by itself otherwise you might get thrown for a loop because it had some additional rare hardware or software with it that raised the value) and you can see what you think is worth your time. Certain models of common systems are also more rare than others. Take a Ti99/4a for example which is worth a case of beer generally. If you happen to find the more elusive ti99/4 (without the a and with a different keyboard) it's worth a lot more even though it's an older system and technically worse than the 99/4a. It's all about how many sold and how many are still out there with those.