The more plants that you have available for sale in your nursery, the quicker they will go out the door. Also, the current health of the plant available for sale will also affect whether or not your customers are willing to buy the plant. I've discovered, that as long as the plants are healthy and you have a large number of plants available, selling will go well. Patience is the key to this. It definitely gets annoying when you're sitting on that one plant that no one seems to want, so either I just wait till I have more plants to sell or I'll just sit in the nursery screen waiting for some sweet customer to love the plant and take it home. Overall, I try not to mess too much with the pricing on the plant, at least I try not to lower it below the suggested price to begin with. Just have a little patience and you'll be okay. Definitely wait until the plant produces all of the seed possible (typically between 4-5) then sell it and continue to do this till you have money built up to buy better items. Hope this helps, if you have any more questions just ask!