One thing to remember with hashtags is there's no point using them, if people aren't searching for them, or they aren't trending. It just makes your tweets look spammy.
In my experence, selling on Twitter isn't ideal. People are on Twitter to see what's going on in the world. To see what news is trending, to see what their friends are doing, to read funny/educational tweets etc. They don't have their debit card in hand, ready to buy something.
If you don't have anybody following you, it'll of course be difficult. Which is why people buy Retweets from larger accounts, as it can kick start their account and bring in real followers - people who follow you because they want to.