Been to a large number and we are in an urban area of 1 million. You wont get fantastic prices. Your best will be cherry picked and very low prices (ala garage sale prices) will be expected. One woman advertised on Craigslist and had a multi day sale. Her fabrics were all LQS quality and mostly Thimbleberry or other high end. She sold for no more than $3 a yard and on the last day a huge amount was left over. I know because I bought three times and spent over $300. Another well advertised high end sale was not well attended and again I think the fabric was around $3 a yard.
Better is to find a guild having a group garage sale or some place where guild members congregate. Maybe place an ad for a month in a guild newsletter. But even the designer of Whimsicals who brought enough to cover a banquet table stacked high only got around $3 a yard and some was left.
You wont make any money reselling fabric unless you are buying at a wholesale level and manage to sell slightly above that amount. I retired from IRS and there is little to know about such sales, except that personal losses are not deductible and only the net recieved over the cost is in any way taxable and it is not likely you will receive anywhere near the amount you paid for it. ("I did pay quilt a bit for it.")