1. when no guests in map => no storefront staff stand by
2. better price
- original PurchasingCost(silver)=MarketValue * Min(0.72 * (1 + (sellerTPI-buyerTPI)), 0.9);
- new PurchasingCost(silver)=MarketValue * Min(0.7 * (1 + (sellerTPI*2-buyerTPI)), 1.0);
- 15 socialLv seller against 0 socialLv buyer = 100% MarketValue !!!
3. buyer will keep 100 silver in inventory when price above the buyer budget
