OK, let's go through this logically (and this follows a discussion with my wife about us buying your company and she vetoed the idea immediately, as it is not even peripheral to what we do) -
VBA - So imagine that I were to buy your operation and I had to integrate it into the current structures. The three things I said were wrong, remain more or less wrong, starting with VBA - it ain't how we do things and any buyer would need to be able to integrate your business into their existing systems, be that slightly goofy GnuCash or a more adult SAP system. Farting about with spreadsheets and some boiled down version of Visual Basic for just one part of the business is really not an option.
When I sold my news agency, one of the many things our advisor told me to fix was to get rid of my brilliant and remarkably simple article database. Our articles, tens-of-thousands of them, were valuable and one of the reasons we managed to get a good price for the company. I and my employees thought our dBase system was just 'triffic - but it was based all on Word Perfect/dBase-III and therefore could not be integrated into Quark-Xpress or Adobe, so out it had to go!
One Supplier - One supplier is deadly! Trust me on that one. Back in 2000, I contacted a German company called SEH about selling their computers in the UK and could have been a good peripheral activity to what we do in the UK. Their prices were good, the quality was good and they could spec them up to have UK Windows and keys, etc. Everything was ready to roll and we knew them and had been selling their stuff in Germany for seven or eight years.
Suddenly Poof! They were gone! Bang - disappeared totally, after a supplier had been caught selling smuggled CPU chips - the Finanzamt came to SEH as the next 'down-the-line' and demanded DM60m with immediate effect and despite being a healthy company with healthy profits and many employees, they had to do the old 'White-Eared Elephant'.
Companies can and do vanish! One supplier has to become many suppliers.
Customer Structure -
@JamieM has already said it all, pretty much. One fulfilment centre should take all that crap off your hands and allows you to do more amusing and/or productive things. If I were to buy your company (see wife's veto above!) the very, very last thing I want to do is waste my time wrapping parcels and solving Amazon's loading bay problems for them! I'm looking for things that are either fun to do or give me a RoI.
An investor is looking for things to invest in. People who are looking for a job do not have money and you need to find people with money or at least people who know how to integrate your company into their structures and are prepared to pay you from post-sale profits with a min. guarantee.
And now for the rest of my grossly unqualified thoughts -
Given the existing two-man structure, that £100k gross profit is whittled down to £20k-£30k gross profit, after employing two people to run the thing.
I would be looking to add value by expanding the company into France and Germany with French and German websites and fulfilment.
My 30 cents worth - keep the company and follow
@JamieM's advice!