Keep an eye out for certain items that can be bought from general/weapons stores and are either not listed on market or listed at a high price. For example, the throwing dagger you can buy from weap store in cc is listed at over 2500% each on market. Now get your fighter to buy a bunch from weapon store and list at 1 silver under the lowest current offer or (in this case at 2050 silvers if non-sub) and buy the lot with your digger.
Another method is using a higher lvled piece of armour, to sell cheap/buy high/repeat, but this involves risk of it being snatched and takes a long time waiting for price to drop.
Another method is buying out all the 50% items listed on market which often happens when it has been listed by 20 different characters (this bumps off the higher listed price items). In this case, simply list at the highest possible offer (2500% for non-subs and 3000% is you're a sub). For example, there are 400 odd disprosiums on market at 50% each, buy them out and list at 62500 each with fighter and buy with digger.