EDIT modified to reflect OP's clarification (in comment here) that these potential buyers are looking to re-sell the software
Re-sellers are going to be looking for three things:
- Is anyone going to make something better, cheaper or more quickly?
- Is this guy going to be able to use our investment effectively to produce more?
- Can we sell what this guy has produced, and will produce?
How to address points 1 and 2 have been very well addressed in other answers, but it's question 3 which is the hardest to prove for us techie people. It's also extremely important - if you can go to these buyers and hand them 3 killer benefits which they can repeat with more flair and Powerpoint when they're doing their sales calls, you'll be off to a good start :)
The main thing you have to do is to take a step back from your work and look at the:
- features: what does it do
- advantages: why is it better
- benefits: why should the customer care
Features are closest to what you care about as a developer, but are pretty much irrelevant to non-technical buyers. Advantages are an essential step in understanding your competition and the customers' alternatives.
By putting features and advantages together, you can hit the customer with a number of benefits, e.g.:
- using my software will save you $0.01 per transaction, or $40,000 p.a.
- my software will increase customer retention by 5%
- your admins will need 15% less time to deploy changes using my software
These are the things that customers care about: what's going to be good for the company, and good for them.
To be brutally honest: the end customer don't care how much effort you put into it (LoC or any other metric), they don't care how well it's written (comments, tests, any other metric), they don't care how hard a problem it is to solve, they don't care about features.
Their only requirement is that it will save them time / effort / money. You know that how hard you've worked to solve the problem, and solve it well, is key to their requirement, but it's secondary. You need to make it perfectly clear why them buying their stuff will mean they'll get promoted.