Pick a race with a small number of runners, say 5. Fill 50 envelopes with the name of horse number 1,with a note saying when this horse wins meet me tomorrow at 1pm and I'll sell you another tip. 50 with horse No2 meet me at 2pm etc.Go to a busy location and hand out as many sealed envelopes as you can. Next day you will have 50 eager customers ready to buy your tips.