Yes you can my friend.In fact,I just sold 50k lobsters yesterday.Only played for about 6 hours. Try selling them in World 1 at South of Varrock West bank.There are a few people who buy them in bulks.If not,they will buy in increments of 100.Here you can sell for 230 each. If you want to get more profit per lobs,I suggest selling them in Edgeville PKing world(3,4 and 5).Here,you can sell them for 240-250 gp each.But do take a note,they will not buy in bulk.