Unfortunately, there are only a few scenarios where a quick/fast flip happens:
You used a $1 to $3 promotion on a semi-decent hand registered domain and flip it for $10 to $20
You scored a better semi-decent dropping domain for less than $50 and flip it for $60 to $90
You scored a lower quality liquid domain for less than the floor liquid value and flip it at a 50% to 100% markup
You scored a super-premium liquid domain for 25% of it's floor value and flip it for 50% (25% markup)
In all the above cases, it takes years of hands on experience and research to pull those off effectively. And even then, 10 to 20 years later, you may still be holding the domain bag with no buyer yet for some of them.
regrettably, this really isn't a get rich quick investment model.
I think you should Hire a domain broker (like GoDaddy or MediaOptions) to handle the sale for you. They reach out to potential buyers, also Negotiate and Speed up the process through their network