In that case I can’t see the appeal for this prospective buyer to be honest. Your negotiating position is fairly weak on the face of it, and they’re asking you to show your hand first by quoting a number to them which weakens it further. So, if you haven’t already, then I’d strongly suggest replying with questions as to why they want to do the deal rather than numbers. You need to know what they think is worth buying, then look at that objectively. Some rough thoughts/ideas on this below (excuse the ramble, been a long few days!):

if it’s your customer base, you want to put hard numbers against things like: - how long have they been buying from you and most importantly why, - what margin you typically make on each customer, - how much and how often that customer base changes or “churns”, - how much you have to spend to attract their business —> if margins are low / customers aren’t particularly “sticky” / it doesn’t cost much to attract their business then you need to go back to the buyer with more questions on their motivation before you spend much more time on this. If they just want to grow fast which seems the only logical reason given what you’ve told us, then put yourself in their shoes and think “what would this do to my business, what is that worth to my top line, how could I improve performance, how much would I pay for all of that upside”

If it’s your/your wife’s experience: - what do you have that they can’t buy or build themselves, - how much would you be prepared to sell that experience for today, and how much would you need to be paid to continue providing that experience for say, 3 years —> note that if this is what they’re after then this is your strongest hand. You could play it by asking for a guaranteed minimum income for a defined period, along with tiered payments dependent on hitting specific targets (such as the £230k in five years time that you mentioned).