No way it's worth $100 million.
Both domains are for different 'markets' market dot com is more retail or for a company wanting to be the new eBay, whereas marketing dot com is what it is 'marketing'.
Owning a single word 'ing' domain myself in finance, I've done a bit of research on 'ing' domains.
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Shopping dot com – Bought by eBay for $634 million
Booking dot com – World known brand
Betting dot com – undisclosed, possible 8 figure domain sale
Gambling dot com – Sold for $2.5 million
Investing.com – Sold for $2.4 million
Savings dot com – Sold for $1.9 million
MarketingToday dot com – Sold for $1.5 million
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Looking at the above sales, $2.5m seems about right.
On getting an idea of Market dot com's value, i would compare it to these domains:-
Insurance dot com - $35.6 million
Money dot com - $24.9 million
Insure dot com - $16 million
Fund dot com - $9,999,950 million
Loans dot com - $3 million
CreditCards dot com - $2.75 million
Coupons dot com - $2.2 million
Mortgage dot com - $1.8 million
Auction dot com - $1.7 million
Deposit dot com - $1.5 million