Its not a question of whether they will buy.
The question is at what price they will buy, and can you make a profit at that price, once your costs of packing, shipping and payment processing are deducted.
Most active plumbers will already have the hand tools that they need on a day to day basis. If they lose one they won't fanny around searching the internet, they are likely to replace them the next time they are in a stockists.
So therefore you are trying to sell them a spare tool, or perhaps an extra tool for the apprentice.
To motivate someone to make a non-urgent tool purchase, they will normally need a deal that gives them a good saving over normal trade prices. It will probably also need to be a bit of extra discount to allow for the fact that you are an unknown trader, so they are taking a bit of a risk. The faster you want to clear your stock and get your money back, the bigger discount you will need to offer.