When considering freelance opportunities I've always considered that for shorter contract terms, a higher rate should be charged, and for longer terms up to an indefinite full time commitment (ie, a full time role) a lower rate can be assumed. So, a company that expects about 30-60 day commitment/expectation with only a possibility of further projects following would assume a higher contracting rate.
What I'm struggling with is when companies ask about your last long term rate, then assume they'll just have the same rate for a short commitment. How do people normally handle the quoting process around this? What if they ask your rate before committing to whether it is a 30 day or 6 month project expectation? Or, do you just use one averaged rate and take whatever length project they offer?
I've considered asking for a 3-month minimum, but I feel like it alienates clients upfront which I hate to do.
EDIT: This can also apply to a contract-to-hire compared to full time role. I'd assume a 1099 contract-to-hire with no benefits would be a higher rate, but companies want to assume it is the same rate as a full time job, just no commitment.