I use tippex but only I stopped posting entries a while ago. I enter the Mail puzzle solving yo text. Yes more expensive butI have won a few times and most of them you can only enter by text.
I photocopy the grid (on my canon printer) work it all out doing corrections if necessary, and then copy it all onto the real crossword. If you have printer that also does copies this does the trick.
its fiddly but it works .... cut a small strip of newspaper from the same page as your crossword the cut it down to the size of the grid but still in a strip, paste one side with UHU glue or similar, place over the offending word and press down then trim off the surplus, once you have mastered this it is much better than tippex.
Not my idea but someone on here many years ago explained how
Considering the thousands of entries they will receive I doubt if it makes any odds. The first all correct opened crossword wins the money and the rest are binned unopened.
Cupid 04:
I read on AB some years ago that every entry, however received, is given a number and the person/device choosing the winning number will not be aware of the medium used. Might have been Lie-in King?
Seems logical.