nothing much you can do about this. You can try and make the seller enter into a contract where they forfeit a deposit if they pull out of the deal with you, but they are very unlikely to enter into it.
Its just part of the house buying process, always has been , always will be.
As the poster above says you could enter a higher offer, and then pull out just before contract exchange, but you will incur legal fees (unless you just sit on it for a few weeks without instructing a solicitor).
SOme very unscrupulous sellers wait right up until the day of exchange and then just demand an exta £xk because they know you’re mentally committed to buying the property. This happened to my parents on day of exchange, the sellers demanded another £50k, needless to say , they were told to shove it.