Lay at every tick and back at every tick higher.

what are the starting odds for 7+ goals in a match?

It may take 10 minutes to get up to the next price , and it will take a lot longer if there is a goal while you are waiting :)

presumably, the first lay price can be the highest price laid

Yes.

You might Lay at 30 , then be waiting to back @32 , but while you wait there is a goal and now the price is 20 .

What do you do then? Hope there are no further goals and back @32 twenty minutes later?

Or back @20 and accept you are going to lose on that game?

OK a market with better liquidity say o/u 4.5 goals.

Over may be 9s pre kick off; lay it at 9 back it at 9.2, lay it and 9.2 back it at 9.4 etc
goal goes in, price drops.
lay at 5s (est.) back at 5.2, lay at 5.2 back at 5.4
goal goes in, price drops.

You get the idea back and trading the one tick margin consistently all match (using a bot/ trade software obv), would you green up or at least be in a safe position before the 5th goal of each match. Or if there is one, choose a safer market with the same liqudity as the one im suggesting above.

Surely punters already do this.

Also, 50% of the time you would get hit during a trade and 50% you wouldnt get hit I assume.

why not just lay it at 9 at start and back it on 89mins?

now it will not work anymore when you posted this online

You're just scalping? This can be done on any market where there is a reasonable amount of movement. People - or their little electronic helpers - do do this as I see them doing it.