Every offer deserves a counter offer. But if you can put the 100k to use, that is a good option. That is two seed rounds for companies you believe in :-)
Sure, but if they offer $100K that's just too low to take serious, I'd definitely hold out for a multiple of that and make it clear that any trickery will be dealt with harshly. A 5%-er with a grudge is something no company can afford.
