100 sell orders is a big number, but some people can offer more stuff for sell and everybody will benefit if there will be more goods on market.
Maybe it makes sense to extend this limit based on rating, like:
rate 5: 200 orders
rate 3: 50 orders
rate 2: 25 orders
?

Also it would be nice to provide more options for listing period. 7 days becames a burden, when you have a lot of sell orders and need to relist them every week.