I always worry about names like that because RentIN and Renting are a little close, and I wonder how that affects the value and seo, so I have tended to avoid them.
I tell everyone the same, if your happy with £300 or you could use £300, then sell away, if you can afford to wait then wait.
Is £300 their first offer or have you worked up already ?
Its ALWAYS worth working up, When i put offers in on names, my first bid is usually a 'feeler', if the person comes back with 10 times+ my feeler then I don't bother trying, I sometimes make my first reply something like 'I was hoping for a bit more than that to be honest, do you have flexibility on price, as I'm open to negotiation', and see what they say.