The other 2 answers (so far) have very good points. But it really depends on what the offer is. My strategy would be to get an actual offer from them and then review the different options. The fact that you have an offer from a company would be very enticing for investors to put money into it for you to build out, if you decide.

This is exactly the strategy I utilized in my own company. We built a solution for one client as a consultant. Wasn't meant for it to be distributed. This client shared what we build in a large conference and we started to get flooded with offers for us to build other clients a similar solution. When this happened, the major player in the industry came along and offered to purchase the solution. We got them to give us an offer and negotiated to a higher price but it wasn't good enough. We used their offer to fundraise and was able to get the company to a valuation 10 times the original offer only 2 years into it. Having said that, if we received a higher offer in the beginning, we probably would've sold it.

I'm a tech entrepreneur (just started another company) that started my career in management consulting. Feel free to reach out if you have further questions or needs.